B.Sc. Second Year�Semester-III�Paper Name: – Physiology�Paper No. - VI

SWAMI RAMANAND TIRTH MARATHWADA UNIVARSITY , NANDED

Gramin (ACS)Mahavidyalaya vasantnagar, Kotgyal Tq. Mukhed Dist. Nanded

Dr. S. K. Pawar

Head and professor

Department of Zoology

Syllabus

UNIT- I

1.Digestion :-

Kinds of digestion: – intracellular and extracellular Digestion . Physiology of Digestion in the alimentary canal.Absorption of carbohydrates, Proteins, lipids.

2. Vitamins:-

Sources and Deficiency Diseases of Fat soluble and water soluble Vitamins.

3. Respiration:-

Kinds of respiration:–Direct and indirect respiration. Respiratory organs in Man. Mechanism of Respiration in Man. Transport of O2 and CO2.

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UNIT- II

1. Excretion:-

Structure of Kidney, Structure of Nephron . Mechanism of Urine formation (ultra filtration and tubular re- absorption).Counter current Mechanism.

2. Cardiovascular System :-

Composition and function of blood . Types of heart in Vertebrates :- Neurogenic and Myogenic Heart. Structure and working of Human Heart . Origin and conduction of the cardiac impulse, Cardiac cycle. E. C. G. and Blood Pressure.

UNIT- III

1. Nerve Physiology:-

Structure of generalized neuron Types of neurons . Structure of synapse . Major Neurotransmitters- Acetyl choline, Adrenaline and dopamine. Conduction of nerve impulse.

2. Muscle Physiology:-

Types of muscles:- smooth muscles, skeletal muscles and cardiac muscles . Ultra structure of skeletal muscles.

UNIT- IV

1. Reproduction:-

Histological Structure of human testes and Ovaries . Physiology of male reproduction:- hormonal control of Spermatogenesis Physiology of female reproduction:- hormonal control of Oogenesis , Menstrual cycle and pregnancy.

2. Endocrine Glands :-

Structure functions and hormonal disorders of:– Pituitary gland, Thyroid gland, Adrenal gland, Islet’s of Langerhans (Pancreas)

UNIT-I

Physiology:-

Physiology:-� Introduction:-�1. The branch of biology that deals with the functions and activities of life or of living matter� (such as organs, tissues, or cells) and of the physical and chemical phenomena involved.�2. The organic processes and phenomena of an organism or any of its parts or of a particular bodily process�

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• Physiology is the science of life.
• It is the branch of biology that aims to understand the mechanisms of living things, from the basis of cell function at the ionic and molecular level to the integrated behavior of the whole body and the influence of the external environment.

•  Physiology is an experimental science.

• The scientific study of an organism's vital functions, including growth and development, the absorption and processing of nutrients, the synthesis and distribution of proteins and other organic molecules, and the functioning of different tissues, organs, and other anatomic structures.
• Physiology studies the normal mechanical, physical, and biochemical processes of animals and plants.

Digestion:-

Digestion:-

• Digestion is how your body turns food you eat into nutrients it uses for energy, growth, and cell repair.
• The digestive tract is a long twisting tube that starts at your mouth and ends at your anus.
• It's made up of a series of muscles that coordinate the movement of food and other cells that make enzymes and hormones to break down food.
• Along the way are three other organs that are needed for digestion: your liver, gallbladder, and pancreas.
• Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma.
• In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream.

What Is the Digestive System:-

• The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining waste.
• Most of these organs make up the gastrointestinal tract.
• Food actually passes through these organs.
• The rest of the organs of the digestive system are called accessory organs.
• These organs secrete enzymes and other substances into the tract, but food does not actually pass through them.

Functions of the Digestive System:-

• The digestive system has three main functions relating to food:- digestion of food, absorption of nutrients from food, and elimination of solid food waste.
• Digestion is the process of breaking down food into components the body can absorb.
• It consists of two types of processes:- mechanical digestion and

chemical digestion.

• Mechanical digestion is the physical breakdown of chunks of food into smaller pieces.
• This type of digestion takes place mainly in the mouth and stomach.
• Chemical digestion is the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by body fluids.
• This type of digestion begins in the mouth and continues in the stomach but occurs mainly in the small intestine.
• After food is digested, the resulting nutrients are absorbed.
• Absorption is the process in which substances pass into the blood stream or lymph system to circulate throughout the body.
• Absorption of nutrients occurs mainly in the small intestine.
• Any remaining matter from food that is not digested and absorbed passes out of the body through the anus in the process of elimination.

Mechanical and Chemical Digestion:-

• There are two kinds of digestion:  mechanical and chemical.
•   Mechanical digestion involves physically breaking the food into smaller pieces. 
• Mechanical digestion begins in the mouth as the food is chewed. 
•  Chemical digestion involves breaking down the food into simpler nutrients that can be used by the cells.
• Chemical digestion begins in the mouth when food mixes with saliva.
•   Saliva contains an enzyme (amylase) that begins the breakdown of carbohydrates. 
• (An enzyme is a protein that can catalyze certain biochemical reactions).

Kinds of digestion:-

• The Digestive Process:- is consist of

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1. Mouth :-

2. Pharynx :-

3. Oesophagus :-

4. Stomach :-

5. Small intestine :-

6. Large intestine :-

7. Rectum :-

• Accessory Organs:-

1. Liver:-

2. Gall bladder:-

3. Pancreas:-

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Mouth:-

• Food is chewed into smaller pieces.
• Adults have 32 specialized teeth—teeth that can grind, chew, and tear different kinds of food.
• The tongue is an organ consisting of skeletal muscles that move the food around the mouth to allow for efficient mechanical digestion.
• Salivary glands beneath and in back of the tongue secrete the saliva that allows for easier swallowing of food and the beginning of chemical digestion. 

Pharynx:-

• Swallowing forces the chewed food through a tubular entrance to the oesophagus.
•  As food is swallowed a flap-like valve, the epiglottis, closes over the trachea to prevent food entering the windpipe and causing choking.  

Oesophagus:-

• The oesophagus connects the pharynx with the stomach. 
• Contractions of the oesophagus push the food through a sphincter  and into the stomach

Stomach:-

• The stomach is a muscular and stretchable sac with three important functions:-
• 1) It mixes and stores food until it can be further digested.
• 2) It secretes chemicals that help break the food into more digestible forms.
• 3) It controls the passage of food into the small intestine.
• The stomach starts chemical digestion of protein. 
• Secretions from the stomach lining consist of about two liters of hydro chloric acid (HCl), pepsin, and other fluids that make up gastric fluids each day.
• The fluid is extremely acidic and it helps kill bacteria and other pathogens that may have been ingested.
• The thick mucus also produced by the stomach lining usually keeps the acids from damaging the lining.
• If not enough mucus is produced or if too much acid is produced, peptic ulcers form. 
• Heredity, stress, smoking, and excessive alcohol intake can make the ulcers worse.
• The condition can worsen and bleeding ulcers can result. 
• Food stays in the stomach for approximately 3-4 hours and moves through another sphincter muscle to pass into the small intestine.

Small intestine:-

• Nearly 7 meters in length, the small intestine is folded and curled around a small area in the abdominal cavity.
• The inside surfaces of the intestine are covered with projections called villi.
• These finger-like structures are covered in smaller projections called microvilli and work to absorb food molecules that have been broken down by the processes of chemical digestion.
• The small intestine has three distinct parts:  the duodenum, the jejunum, and the ileum. 
• Each day, about 9 liters of fluid enters the duodenum. 
• Most chemical digestion takes place in the duodenum by chemicals secreted by the liver, pancreas and small intestine.
• The other two sections of the small intestine, the jejunum and the ileum, absorb food molecules by way of the villi directly into the blood stream.

Large intestine:-

• The large intestine receives the material “left-over” from chemical digestion that is basically nutrient free.
• Only water, cellulose, and undigestible materials are left.
• The main job of the large intestine is to remove water from the undigested material.
• Water is quickly removed from the material through villi and returns to the blood stream.  

Rectum:-

• The last part of the digestive tract is the rectum, a “holding area” for the undigested material.
• Waste leaves the body from this area.

Accessory Organs:-

Liver:-

• The liver is a large organ located just above the stomach. 
• The liver produces bile which helps digest lipids. 
• Bile is stored in the gallbladder and flows from the gallbladder to the duodenum where it helps digest fats.
• The picture at the left shows a human liver.

Gall bladder:-

• The gall bladder is a small, greenish organ located just under the liver.
• It stores bile produced by the liver until it is secreted directly into the first section of the small intestine.

Pancreas:-

• The pancreas has three important functions that help the digestive system change food into a form that can be used by the cells.

1) It produces enzymes which help break down proteins, lipids, and carbohydrates.

2) It produces the hormone, insulin, which helps regulate blood glucose levels.

3) It produces sodium bicarbonate which helps to neutralize stomach acids.

Intracellular digestion:-

• Every organism requires energy to be active.
•  However, to obtain energy from its outside environment, cells must not only retrieve molecules from their surroundings but also break them down.
•  This process is known as intracellular digestion.
•  In its broadest sense, intracellular digestion is the breakdown of substances within the cytoplasm of a cell.
• Intracellular digestion can also refer to the process in which animals that lack a digestive tract bring food items into the cell for the purposes of digestion for nutritional needs.
• This kind of intracellular digestion occurs in many unicellular protozoans.

Intracellular Digestion:-

• The simplest example of digestion intracellular digestion, which takes place in a gastrovascular cavity with only one opening.
• Most animals with soft bodies use this type of digestion, including Platyhelminthes (flatworms), Ctenophora (comb jellies), and Cnidaria (coral, jelly fish, and sea anemones).
• The gastrovascular cavities of these organisms contain one open which serves as both a “mouth” and an “anus”.

• Ingested material enters the mouth and passes through a hollow, tubular cavity.
• The food particles are engulfed by the cells lining the gastrovascular cavity and the molecular are broken down within the cytoplasm of the cells (intracellular).

Function:-

• Intracellular digestion is divided into heterophagy digestion and autophagic digestion.
• These two types take place in the lysosome and they both have very specific functions.
•  Hetero phatic intracellular digestion has an important job which is to break down all molecules that are brought into a cell by endocytosis.
•  The degraded molecules need to be delivered to the cytoplasm; however, this will not be possible if the molecules are not hydrolyzed in the lysosome.
• Autophagic intracellular digestion is processed in the cell, which means it digests the internal molecules.

Extracellular Digestion:-

• The alimentary canal is a more advanced digestive system than a gastrovascular cavity and carries out extracellular digestion.
• Most other invertebrates like segmented worms (earthworms), arthropods (grasshoppers), and arachnids (spiders) have alimentary canals.
• The alimentary canal is compartmentalized for different digestive functions and consists of one tube with a mouth at one end and an anus at the other.
• Once the food is ingested through the mouth, it passes through the oesophagus and is stored in an organ called the crop; then it passes into the gizzard where it is churned and digested.
• From the gizzard, the food passes through the intestine and nutrients are absorbed.
• Because the food has been broken down exterior to the cells, this type of digestion is called extracellular digestion.
• The material that the organism cannot digest is eliminated as feces, called castings, through the anus.
• Most invertebrates use some form of extracellular digestion to break down their food.
• Flatworms and cnidarians, however, can use both types of digestion to break down their food.

Extracellular Digestion:- 

• Since digestion occurs outside the cell, it is said to be extracellular.
• It takes place either in the lumen of the digestive system, in a gastric cavity or completely outside the body.
• The prefix "extra" means "outside the thing ", and indicates that extracellular digestion must occur outside the cell.
• During extracellular digestion, food is broken down outside the cell either mechanically or with acid by special molecules called enzymes.
• Once the food is broken down extracellularly into nutrients, the cells of the hydra can absorb it for energy.
• Extracellular digestion is a form of digestion found in all

haplobiontic annelids, crustaceans, arthropods, lichens and chordates, including vertebrates.

Physiology of digestion in the alimentary canal:-

• The function of the digestive system is to break down the foods you eat, release their nutrients, and absorb those nutrients into the body.
• Although the small intestine is the workhorse of the system, where the majority of digestion occurs, and where most of the released nutrients are absorbed into the blood or lymph, each of the digestive system organs makes a vital contribution to this process.

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Physiology of digestion in the alimentary canal:-

• As is the case with all body systems, the digestive system does not work in isolation; it functions cooperatively with the other systems of the body.
• Consider for example, the interrelationship between the digestive and cardiovascular systems.
• Arteries supply the digestive organs with oxygen and processed nutrients, and veins drain the digestive tract.
• These intestinal veins, constituting the hepatic portal system, are unique; they do not return blood directly to the heart.
• Rather, this blood is diverted to the liver where its nutrients are off-loaded for processing before blood completes its circuit back to the heart.
• At the same time, the digestive system provides nutrients to the heart muscle and vascular tissue to support their functioning.
• The interrelationship of the digestive and endocrine systems is also critical.
• Hormones secreted by several endocrine glands, as well as endocrine cells of the pancreas, the stomach, and the small intestine, contribute to the control of digestion and nutrient metabolism.
• In turn, the digestive system provides the nutrients to fuel endocrine function.

Digestive System Organs:-

• The easiest way to understand the digestive system is to divide its organs into two main categories.
• The first group is the organs that make up the alimentary canal.
• Accessory digestive organs comprise the second group and are critical for orchestrating the breakdown of food and the assimilation of its nutrients into the body.
• Accessory digestive organs, despite their name, are critical to the function of the digestive system.

Alimentary Canal Organs:-

• Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = “to nourish”) is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured after death, once smooth muscle tone is lost.
• The main function of the organs of the alimentary canal is to nourish the body.
• This tube begins at the mouth and terminates at the anus.
• Between those two points, the canal is modified as the pharynx, oesophagus, stomach, and small and large intestines to fit the functional needs of the body.
• Both the mouth and anus are open to the external environment; thus, food and wastes within the alimentary canal are technically considered to be outside the body.
• Only through the process of absorption do the nutrients in food enter into and nourish the body’s “inner space.”

Accessory Structures:-

• Each accessory digestive organ aids in the breakdown of food.
• Within the mouth, the teeth and tongue begin mechanical digestion, where as the salivary glands begin chemical digestion.
• Once food products enter the small intestine, the gall bladder, liver, and pancreas release secretions—such as bile and enzymes—essential for digestion to continue.
• Together, these are called accessory organs because they sprout from the lining cells of the developing gut and augment its function; indeed, you could not live without their vital contributions, and many significant diseases result from their malfunction.
• Even after development is complete, they maintain a connection to the gut by way of ducts.

Nerve Supply:-

• As soon as food enters the mouth, it is detected by receptors that send impulses along the sensory neurons of cranial nerves.
• Without these nerves, not only would your food be without taste, but you would also be unable to feel either the food or the structures of your mouth, and you would be unable to avoid biting yourself as you chew, an action enabled by the motor branches of cranial nerves.
• Intrinsic innervation of much of the alimentary canal is provided by the enteric nervous system, which runs from the oesophagus to the anus, and contains approximately 100 million motor, sensory, and interneurons.
• These enteric neurons are grouped into two plexuses.
• The myenteric plexus lies in the muscularis layer of the alimentary canal and is responsible for motility, especially the rhythm and force of the contractions of the muscularis.
• The submucosal plexus lies in the submucosal layer and is responsible for regulating digestive secretions and reacting to the presence of food.
• Extrinsic innervations of the alimentary canal are provided by the autonomic nervous system, which includes both sympathetic and parasympathetic nerves.
• In general, sympathetic activation restricts the activity of enteric neurons, there by decreasing GI secretion and motility.
• In contrast, parasympathetic activation increases GI secretion and motility by stimulating neurons of the enteric nervous system.

Blood Supply:-

• The blood vessels serving the digestive system have two functions.
• They transport the protein and carbohydrate nutrients absorbed by mucosal cells after food is digested in the lumen.
• Lipids are absorbed via lacteals, tiny structures of the lymphatic system.
• The blood vessels’ second function is to supply the organs of the alimentary canal with the nutrients and oxygen needed to drive their cellular processes.
• Specifically, the more anterior parts of the alimentary canal are supplied with blood by arteries branching off the aortic arch and thoracic aorta.
• Below this point, the alimentary canal is supplied with blood by arteries branching from the abdominal aorta.
• The celiac trunk services the liver, stomach, and duodenum, where as the superior and inferior mesenteric arteries supply blood to the remaining small and large intestines.
• The veins that collect nutrient-rich blood from the small intestine empty into the hepatic portal system.
• This venous network takes the blood into the liver where the nutrients are either processed or stored for later use.
• Only then does the blood drained from the alimentary canal viscera circulate back to the heart.
• To appreciate just how demanding the digestive process is on the cardiovascular system, consider that while you are “resting and digesting,” about one-fourth of the blood pumped with each heartbeat enters arteries serving the intestines.

The Peritoneum:-

• The digestive organs within the abdominal cavity are held in place by the peritoneum, a broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue.
• It is composed of two different regions: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the abdominal organs.
• The peritoneal cavity is the space bounded by the visceral and parietal peritoneal surfaces.
• A few milliliters of watery fluid act as a lubricant to minimize friction between the serosal surfaces of the peritoneum.

Absorption of carbohydrates:-

1. Glucose and Galactose:-

• They  are transported from the intestinal lumen into the cells by a Na+-dependent co-transport (SGLT 1) in the luminal membrane.
• The sugar is transported “uphill” and Na+ is transported “downhill.”
• They are then transported from cell to blood by facilitated diffusion (GLUT 2).
• The Na+–K+ pump in the basolateral membrane keeps the intracellular [Na+] low, thus maintaining the Na+ gradient across the luminal membrane.

2. Fructose

• Fructose   is transported exclusively by facilitated diffusion; therefore, it cannot be absorbed against a concentration gradient.

Absorption of Proteins:-

1. Free amino acids:-

•   Na+-dependent amino acid cotransport occurs in the luminal membrane.
• It is analogous to the cotransporter for glucose and galactose.
• The amino acids are then transported from cell to blood by facilitated diffusion.
• There are four separate carriers for neutral, acidic, basic, and amino acids, respectively.

2. Dipeptides and tripeptides:-

• They are absorbed faster than free amino acids.
•   H+-dependent cotransport of dipeptides and tripeptides also occurs in the luminal membrane.
•  After the dipeptides and tripeptides are transported into the intestinal cells, cytoplasmic peptidases hydrolyze them to amino acids.
• The amino acids are then transported from cell to blood by facilitated diffusion.

Absorption of Fats (Lipids):-

• Micelles bring the products of lipid digestion into contact with the absorptive surface of the intestinal cells.
• Then, fatty acids, monoglycerides, and cholesterol diffuse across the luminal membrane into the cells.
• Glycerol is hydrophilic and is not contained in the micelles.
• In the intestinal cells, the products of lipid digestion are re-esterified to triglycerides, cholesterol ester, and phospholipids and, with apoproteins, form chylomicrons.
• Chylomicrons are transported out of the intestinal cells by exocytosis.
• Because chylomicrons are too large to enter the capillaries, they are transferred to lymph vessels and are added to the bloodstream via the thoracic duct.

2. Vitamins:-

• A vitamin is an organic molecule  that is an essential micronutrient which an organism needs in small quantities for the proper functioning of its metabolism.
• Essential nutrients cannot be synthesized in the organism, either at all or not in sufficient quantities, and therefore must be obtained through the diet.
• The term vitamin does not include the three other groups of essential nutrients: minerals, essential fatty acids, and essential amino acids. 
• Most vitamins are not single molecules, but groups of related molecules called vitamers.
• Some sources list 14 vitamins, by including , but major health organizations list 13 : vitamin A , vitamin B₁, vitamin B₂ , vitamin B₃ , vitamin B₅ , vitamin B₆ , vitamin B₇, vitamin B₉ vitamin B₁₂, vitamin C, vitamin D , vitamin E and vitamin K .

The Fat-Soluble Vitamins: A, D, E and K:-

• Vitamins can be classified based on their solubility.
• Most are water-soluble, meaning they dissolve in water.
• In contrast, the fat-soluble vitamins are similar to oil and do not dissolve in water.
• Fat-soluble vitamins are most abundant in high-fat foods and are much better absorbed into your bloodstream when you eat them with fat.
• There are four fat-soluble vitamins in the human diet:

Vitamin A

Vitamin D

Vitamin E

Vitamin K

• The comprehensive overview of the fat-soluble vitamins, their health benefits, functions and main dietary sources article provides as.

Vitamin A:-

• Vitamin A plays a key role in maintaining your vision. Without it, you would go blind.

Types

• Vitamin A is not a single compound. Rather, it is a group of fat-soluble compounds collectively known as retinoids.
• The most common dietary form of vitamin A is retinol. Other forms — retinal and retinoic acid — are found in the body, but absent or rare in foods.
• Vitamin A2 (3,4-dehydroretinal) is an alternative, less active form found in freshwater fish.

Role and Function of Vitamin A

• Vitamin A supports many critical aspects of body function, including:
• Vision maintenance: Vitamin A is essential for maintaining the light-sensing cells in the eyes and for the formation of tear fluid .
• Immune function: Vitamin A deficiency impairs immune function, increasing susceptibility to infections .
• Body growth: Vitamin A is necessary for cell growth. Deficiency may slow or prevent growth in children .
• Hair growth: It is also vital for hair growth. Deficiency leads to alopecia, or hair loss .
• Reproductive function: Vitamin A maintains fertility and is vital for fetal development .

Dietary Sources:-

• Vitamin A is only found in animal-sourced foods.
• The main natural food sources are liver, fish liver oil and butter.

• Vitamin A can also be derived from certain carotenoid antioxidants found in plants.
• They are collectively known as provitamin A.
• The most efficient of these is beta-carotene, which is abundant in many vegetables, such as carrots, kale and spinach .

Vitamin A Deficiency:-

• Vitamin A deficiency is rare in developed countries.
• However, vegans may be at risk, since pre-formed vitamin A is only found in animal-sourced foods.
• Although provitamin A is abundant in many fruits and vegetables, it is not always efficiently converted into retinol, the active form of vitamin A.
• The efficiency of this conversion depends on people's genetics.
• Deficiency is also widespread in some developing countries where food variety is limited.
• It is common in populations whose diet is dominated by refined rice, white potatoes or cassava and lacking in meat, fat and vegetables.
• A common symptom of early deficiency includes night blindness. As it progresses, it may lead to more serious conditions, such as:
• Dry eyes: Severe deficiency may cause xerophthalmia, a condition characterized by dry eyes caused by reduced tear fluid formation.
• Blindness: Serious vitamin A deficiency may lead to total blindness.
• In fact, it is among the most common preventable causes of blindness in the world.
• Hair loss: If you are vitamin A deficient, you may start to lose your hair.
• Skin problems: Deficiency leads to a skin condition known as hyperkeratosis or goose flesh.
• Poor immune function: Poor vitamin A status or deficiency makes people prone to infections .

Vitamin A Toxicity:-

• Overdosing on vitamin A leads to an adverse condition known as hypervitaminosis A.
• It's rare, but may have serious health effects.
• Its main causes are excessive doses of vitamin A from supplements, liver or fish liver oil.
• In contrast, high intake of provitamin A does not cause hypervitaminosis.
• The main symptoms and consequences of toxicity include fatigue, headache, irritability, stomach pain, joint pain, lack of appetite, vomiting, blurred vision, skin problems and inflammation in the mouth and eyes.
• It may also lead to liver damage, bone loss and hair loss.
• At extremely high doses, vitamin A can be fatal .
• People are advised to avoid exceeding the upper limit for intake, which is 10,000 IU (900 mcg) per day for adults.
• Higher amounts, or 300,000 IU (900 mg), may cause acute hypervitaminosis A in adults.
• Children can experience harmful effects at much lower amounts.
• Individual tolerance varies considerably.
• Children and people with liver diseases like cirrhosis and hepatitis are at an increased risk and need to take extra care.
• Pregnant women should also be especially careful, since high doses of vitamin A may harm the fetus.
• Doses as low as 25,000 IU per day have been linked with birth defects.

Benefits of Vitamin A Supplements:-

• While supplements are beneficial for those who suffer from deficiency, most people get enough vitamin A from their diet and do not need to take supplements.
• Yet, controlled studies suggest that vitamin A supplements may benefit certain people even if their diet meets the basic requirements.
• For instance, vitamin A supplements may help treat measles in children.
• They protect against measles-associated pneumonia and reduce the risk of death by 50–80%.
• Studies suggest that vitamin A acts by suppressing the measles virus.

Vitamin D:-

• Nicknamed the sunshine vitamin, vitamin D is produced by your skin when it's exposed to sunlight.
• It is best known for its beneficial effects on bone health, and deficiency makes you highly susceptible to bone fractures.

Types

• Vitamin D is a collective term used to describe a few related fat-soluble compounds.
• Also known as calciferol, vitamin D comes in two main dietary forms:
• Vitamin D2 (ergocalciferol): Found in mushrooms and some plants.
• Vitamin D3 (cholecalciferol): Found in animal-sourced foods, such as eggs and fish oil, and produced by your skin when exposed to sunlight.

Role and Function of Vitamin D:-

• Vitamin D has numerous roles and functions, but only a few are well researched.
• These include the following:
• Bone maintenance: Vitamin D regulates the circulating levels of calcium and phosphorus, which are the most important minerals for bone growth and maintenance.
• It promotes the absorption of these minerals from the diet.
• Immune system regulation: It also regulates and strengthens immune system function.
• Once absorbed into the bloodstream, the liver and kidneys change calciferol into calcitriol, which is the biologically active form of vitamin D.
• It can also be stored for later use in the form of calcitriol.
• Vitamin D3 is more efficiently converted into calcitriol than vitamin D2.

Sources of Vitamin D:-

• Your body can produce all the vitamin D it needs as long as you regularly expose large parts of your skin to sunlight.
• However, many people spend little time in the sun or do so fully clothed.
• Justifiably, others cover their skin with sunscreen to prevent sunburns.
• While sunscreen use is highly recommended, it reduces the amount of vitamin D produced by your skin.
• As a result, people generally need to rely on their diets to get enough vitamin D.
• Few foods naturally contain vitamin D.
• The best dietary sources are fatty fish and fish oil, but mushrooms that have been exposed to ultraviolet light may also contain significant amounts.
• The chart below shows the amounts of vitamin D in 3.5 ounces (100 grams) of some of its richest dietary source:

Vitamin D Deficiency:-

• Severe vitamin D deficiency is rare, but mild forms of deficiency or insufficiency are common among hospitalized people as well as the elderly.
• Risk factors of deficiency are dark skin color, old age, obesity, low sun exposure and diseases that impair fat absorption.
• The most well-known consequences of vitamin D deficiency include soft bones, weak muscles and an increased risk of bone fractures.
• This condition is called osteocalcin in adults and rickets in children.
• Vitamin D deficiency is also associated with poor immune function, an increased susceptibility to infections and autoimmune diseases.
• Other signs of deficiency or insufficiency may include fatigue, depression, hair loss and impaired wound healing.
• Observational studies have also linked low vitamin D levels or deficiency with an increased risk of dying from cancer and an elevated risk of heart attacks.

Vitamin D Toxicity:-

• Vitamin D toxicity is very rare.
• While spending a lot of time in the sun doesn't cause vitamin D toxicity, taking high amounts of supplements may harm you.
• The main consequence of toxicity is hypercalcemia, a condition characterized by excessive amounts of calcium in the blood.
• Symptoms include headache, nausea, lack of appetite, weight loss, fatigue, kidney and heart damage, high blood pressure and fetal abnormalities, to name a few.
• People are generally advised to avoid exceeding the upper limit of vitamin D intake, which is 4,000 IU per day for adults.
• Higher amounts, ranging from 40,000–100,000 IU (1,000–2,500 mcg) per day, may cause symptoms of toxicity in adults when taken daily for one or two months.
• Keep in mind that much lower doses may harm young children.

Benefits of Vitamin D Supplements:-

• For people who spend little time in the sun and seldom eat fatty fish or liver, supplements can be very beneficial.
• Regularly taking supplements seems to prolong people's lives, especially hospitalized or institutionalized elderly people.
• Supplements may also reduce the risk of respiratory tract infections.
• They may also have many other benefits in people with vitamin D deficiency, but more studies need to examine their effects in people with sufficient vitamin D levels.

Vitamin E:-

• As a powerful antioxidant, vitamin E protects your cells against premature aging and damage by free radicals.

Types

• Vitamin E is a family of eight structurally similar antioxidants that are divided into two groups:
• Tocopherols: Alpha-tocopherol, beta-tocopherol, gamma-tocopherol and delta-tocopherol.
• Tocotrienols: Alpha-tocotrienol, beta-tocotrienol, gamma-tocotrienol and delta-tocotrienol.
• Alpha-tocopherol is the most common form of vitamin E.
• It makes up around 90% of the vitamin E in the blood.

Role and Function of Vitamin E:-

• Vitamin E's main role is to act as an antioxidant, preventing oxidative stress and protecting fatty acids in your cell membranes from free radicals.
• These antioxidant properties are enhanced by other nutrients, such as vitamin C, vitamin B3 and selenium.
• In high amounts, vitamin E also acts as a blood thinner, reducing the blood's ability to clot.

Vitamin E Deficiency:-

• Vitamin E deficiency is uncommon and is never detected in people who are otherwise healthy.
• It happens most often in diseases that impair the absorption of fat or vitamin E from food, such as cystic fibrosis and liver disease.
• Symptoms of vitamin E deficiency include muscle weakness, walking difficulties, tremors, vision problems, poor immune function and numbness.
• Severe, long-term deficiency may lead to anemia, heart disease, serious neurological problems, blindness, dementia, poor reflexes and the inability to fully control body movements.

Vitamin E Toxicity:-

• Overdosing on vitamin E is difficult when it is obtained from natural dietary sources.
• Cases of toxicity have only been reported after people have taken very high doses of supplements.
• Yet, compared to vitamin A and D, overdosing on vitamin E appears to be relatively harmless.
• It may have blood-thinning effects, counteracting the effects of vitamin K and causing excessive bleeding.
• Thus, people who take blood-thinning medications should avoid taking large doses of vitamin E.
• Additionally, at high doses of more than 1,000 mg per day, vitamin E may have pro-oxidant effects.
• That is, it can become the opposite of an antioxidant, potentially leading to oxidative stress.

Benefits and Risks of High Vitamin E Intake or Supplements:-

• High vitamin E intake from food or supplements has been linked with a number of benefits.
• One form of vitamin E, gamma-tocopherol, was found to increase blood flow by promoting the dilation of blood vessels, potentially reducing blood pressure and the risk of heart disease.
• Gamma-tocopherol supplements may also have a blood-thinning effect as well as reducing levels of "bad" LDL cholesterol.
• In contrast, other studies suggest that high-dose vitamin E supplements may be harmful, even when they don't cause any obvious symptoms of toxicity.
• For instance, observational studies show that taking vitamin E supplements is linked with an increased risk of prostate cancer and death by all causes.
• Given the potentially adverse effects of vitamin E supplements, they cannot be recommended at this point.
• High-quality studies are needed before solid conclusions can be reached about the long-term safety of these supplements.

Vitamin K:-

• Vitamin K plays a key role in blood clotting.
• Without it, you would run the risk of bleeding to death.

Types

• Vitamin K is actually a group of fat-soluble compounds divided into two main groups:
• Vitamin K1 (phylloquinone): Found in plant-sourced foods, phylloquinone is the main form of vitamin K in the diet.
• Vitamin K2 (menaquinone): This variety of vitamin K is found in animal-sourced foods and fermented soy products, like natto.
•  Vitamin K2 is also produced by gut bacteria in the colon.
• Additionally, there are at least three synthetic forms of vitamin K.
• These are known as vitamin K3 (menadione), vitamin K4 (menadiol diacetate) and vitamin K5.

Role and Function of Vitamin K:-

• Vitamin K plays an essential role in blood clotting.
• In fact, the "K" stands for "coagulation," the Danish word for coagulation, which means clotting.
• But vitamin K has other functions as well, including supporting bone health and helping prevent the calcification of blood vessels, potentially reducing the risk of heart disease.

Dietary Sources:-

• The best dietary sources of vitamin K1 (phylloquinone) are leafy green vegetables, where as vitamin K2 (menaquinone) is mainly found in animal-sourced foods and fermented soy products.
• The table below shows some of the main sources of vitamin K1 and the amounts found in 3.5 ounces (100 grams) of these foods :

Vitamin K Deficiency:-

• Unlike vitamins A and D, vitamin K isn't stored in the body in significant amounts.
• For this reason, consuming a diet lacking in vitamin K may lead you to become deficient in as little as a week.
• People who do not efficiently digest and absorb fat are at the greatest risk of developing vitamin K deficiency.
• This includes those who suffer from celiac disease, inflammatory bowel disease and cystic fibrosis.
• Use of broad-spectrum antibiotics may also raise the risk of deficiency, as well as very high doses of vitamin A, which seem to reduce vitamin K absorption.
• Mega-doses of vitamin E may also counteract the effects of vitamin K on blood clotting.
• Without vitamin K, your blood wouldn't clot and even a small wound could cause unstoppable bleeding.
• Fortunately, vitamin K deficiency is rare, since the body only needs small amounts to maintain blood clotting.
• Low levels of vitamin K have also been linked with reduced bone density and increased risk of fractures in women.

Vitamin K Toxicity:-

• Unlike the other fat-soluble vitamins, natural forms of vitamin K have no known symptoms of toxicity.
• As a result, scientists have not been able to establish a tolerable upper intake level for vitamin K.
• Further studies are needed.
• In contrast, a synthetic form of vitamin K, known as menadione or vitamin K3, may have some adverse effects when consumed in high amounts.

Water soluble vitamins:-

• Water-soluble vitamins consist of the B-group vitamins and vitamin C.
• Their deficiency is treated by administration of the deficient vitamin.

B Group Vitamins Features:-

• A common feature of group B vitamins is their occurrence in yeast (except vitamin B₁₂).
• However, if the yeast is included in the diet only as a means of rising bread, then yeast is not considered the major source of group B vitamins in humans; a small quantity of yeast does not contain nutritionally significant amount of B vitamins.
• Their metabolic effects are inter-linked.
• Deficiency of only a single vitamin occurs rarely.
• They are produced by the intestinal micro flora but the amount produced is generally only a fraction of the daily recommended intake.
• Some are more frequently called by their name, others by number.
• Some vitamins may not have a number because it has been found that some substances, originally considered as vitamins, are NOT essential for humans, therefore they are not vitamins or are a mixture of substances.

Vitamin B₁

Source:-

Meat, fish, cereals, yeast, legumes.

Daily recommended intake for adults: 1-1.4 mg 

Deficiency:-

• The disease beri-beri
• from a lack of dietary vitamin B₁ is found today in very poor population groups in countries where people live mostly on polished/white rice.
• It may also develop in people who live mostly on refined wheat flour products and among alcoholics and food faddists.
• A typical image consists of nervous disorders, especially peripheral nerves ,edema and heart disease.
• Impaired absorption of vitamin B₁ occurs in alcoholics and is manifested by Wernicke encephalopathy.
• Suboptimal thiamine status based on biochemical criteria in Europe was detected only in 4-6% of the population. Risk group are alcoholics.
• Laboratory evaluation: thiamine excretion in the urine.
• In the absence of erythrocytes is reduced transketolase concentration in the blood and the sea is high concentrations of glyoxalase.

Vitamin B2 structure:-

• Riboflavin or vitamin B₂ is part of coenzymes Flavin adenine mononucleotide (FAD) and flavin mononucleotide (FMN), plays a key role in oxidative metabolism.

Source:-

• A small amount is found in many foods.
• Main sources are meat, milk and milk products; good sources are also fish, offal ,eggs, and whole grain cereals.
• Milling of cereals removes most of vitamin B₂ - some countries (e.g. USA) fortify cereal products with riboflavin.

Recommended daily intake for adults: 1.2 to 1.5 mg 

• Deficiency According to several population studies, the deficiency is widespread in developing countries, where diet is poor in animal foods, vegetables and fruits, and where cereals are milled.
• Frequently the deficiency is secondary due to malabsorption, enterocolitis, coeliac disease , chronic hepatitis; in children often after the use of broad-spectrum antibiotics.
• It may develop in cancer, cardiac disease, diabetes
• Clinical picture: The description of the signs of riboflavin deficiency is somewhat inconsistent in various scientific publications.
• Riboflavin deficiency occurs almost always together with deficiencies of other group B vitamins, which may cause some of the signs described in literature The signs most frequently described are: angular stomatitis, peeling lips, glossitis, and normocytic normochromic anemia.
• Laboratory evaluation: decreases secretion of vitamin B₂ in urine , decreased concentrations of glutathione and glutathione reductase in erythrocytes.

• It is part of enzymes, oxide-reduction systems (nicotinamide adenine dinucleotide -NAD, nicotinamide adenine diphosphate -NADP).
• May form in the liver from tryptophan and its biosynthesis is very slow and it is needed vitamin B₆.

Source

• The source of most foods - meat, fish, cereals.
• The recommended daily dose for adults is by age and sex of 13-17 mg
• Niacin (vitamin B₃) is the name for nicotinamide and nicotinic acid.

Deficit

• Disease pellagra is caused by the current lack of niacin and its precursor tryptophan.
• Today it has rarely occurs in a very poor population groups or for refugees in developing countries.

• Occurs in people who eat mostly corn/maize.
• The symptoms are as a mnemonic device used sometimes called "disease of three D"- dermatitis, diarrhea, dementia.
• Surplus Signs of excess food are not known.
• High doses of dietary supplements induce vasodilatation, warmth, gastritis, damage to liver cells.
• Income should not exceed 35 mg / kg / day.

• Pharmacological use Nicotinic acid and its derivatives are used to treat hyperlipidemia by inhibiting the secretion of VLDL from the liver and increasing the activity of peripheral lipoprotein lipase.
• This leads to a reduction in circulating VLDL and, consequently, LDL( cholesterol ).
• In contrast adipose tissue blocking the intracellular lipase , thus releasing the MK inventory, further reducing supply to the liver TAG and reduces VLDL synthesis.
• Adverse effects: harmless vasodilation in the skin associated with subjective stream feeling hot - it can handle submitting aspirin; at 1 / 5 of patients treated with hyperuricemia; skin rash.

Vitamin B₅ (pantothenic acid):-

Source:-

• Small amounts are in almost all foods contain a large amount of yeast, liver, meat, milk, whole grains and legumes.
• The daily recommended dose for adults: 6 mg

Deficit:-

• Lack is not present - described only when administered pantothenic acid antagonists and extremely malnourished people with symptoms of deficiency of other nutrients, is manifested hair follicle atrophy, loss of pigmentation, dermatitis .

Surplus:-

• Signs of excess are not known.

Vitamin B₆ (Pyridoxine):-

• Pyridoxine the name vitamin B₆ comprises a group of compounds.
• It coenzyme for more than 50 enzymatic reactions - decarboxylase and transaminases, synthesis of acid nicotine and arachidonic acid , affects the function of the nervous system, immune reactions and synthesis of haemoglobin.

Source:-

• It is abundant in food.
• The daily recommended dose for adults: 13-17 mg

Deficit:-

• Deficiency with normal eating habits does not occur; manifested skin and mucosal changes that occur rhagades corners, peripheral neuropathy .

Surplus:-

• Excess of food does not occur.
• After a prolonged intake of 50-500 mg have been reported sensory neuropathy.

Vitamin B₇ (Biotin):-

• Biotin Vitamin B₇ , vitamin H, factor R - Several scholars have described it, only later discovered that it is the same substance) is important for the metabolism of amino acids and fatty acids, is a cofactor for carboxylases.

Source:-

• At low concentrations in many foods. Rich sources are yeast, liver, egg yolk, nuts, lentils. The daily requirement (RDA can not be estimated): 30-60 mg

Deficit:-

• Deficiency of food does not occur.
• Scientists described the people who long consumed a large amount of raw eggs and improper parenteral nutrition.
• Symptoms : seborrheic dermatitis , fatigue, anorexia , nausea ,hypercholesterolemia , vascular disorders.

Surplus:-

• Signs of excess are not known.

Vitamin B₉ (Folic acid):-

• folic acid also is known as vitamin B₉, folate or folacin .
• Includes a group of compounds: Folic Acid and folic acid.
• Along with vitamin B₁₂ is essential for the formation of nucleic acids and thus for synthesis of DNA , participate in the transfer radicals and in all processes of cell division , it is important for cell division and tissue with high mitotic activity.
• Absorbed in the proximal parts of the small intestine and when excess it is excreted in the urine.

Source:-

• Liver, yeast, green leafy vegetables, as well as whole grain cereals, meat, milk, eggs and legumes.
• The recommended daily adult dose: 400mg.
• In pregnancy, 600mg for prevention of congenital malformations (mainly cleft neural tube).

Deficit:-

• Deficiency of vitamin B₉ occurs in low supply, absorption or increased need during pregnancy.
• There is a megaloblastic anemia , which is characterized by the presence of abnormal precursors of red blood cells in the bone marrow.
• Compared with normal cells are cells arising from these abnormal precursors of different shape, larger size, reduced viability and reduced ability to transport oxygen .
• Along with the lack of iron is its lack of a significant cause of anemia in developing countries. Deficiency during pregnancy causes spina neural tube in the fetus.
• Laboratory evaluation: serum levels of folate, total homocysteine.

Surplus:-

• High intake of folic acid can mask vitamin B₁₂ , so the upper limit of the daily recommended intake of up to 1000 mg / day.

Vitamin B₁₂ (cobalamin):-

• Vitamin B₁₂(cobalamin) is the collective name for several compounds that are in the center of porphyrin skeletal cobalt .
• Vitamin B₁₂ has a number of biological functions - plays an important role in hematopoiesis, is essential for the development of the central nervous system in children, contributes to the formation of nucleic acids , transmethylation marches and has anabolic effect.
• Deficiency of vitamin B₁₂ in adults causes macrocytic anemia , impaired rear and lateral spinal cords, peripheral nerves and dementia or depression .
• Lack of vitamin B₁₂ also affects secondary folate cycle resulting in impaired synthesis of purines and pyrimidines necessary for the formation of DNA and RNA.
• Source:-
• In nutritionally significant quantities occurs only in animal foods.
• Rich sources are liver, kidney, meat warm-blooded animals (1-2 ìg/100 g), fish, egg yolk and dairy products (milk ìg/100, 0.3 ml cheese ìg/100 0.2 to 0.6g).

• Plant foods contain trace amounts of vitamin B₁₂ only if it has been processed by bacterial fermentation.
• Absorbed in the small intestine only if the stomach creates a complex with an internal factor .
• Therefore it is necessary to properly functioning stomach and large amounts of vitamin B₁₂ are formed by the intestinal flora in humans unusable.
• Cobalamin with an internal factor in the distal ileum bind to specific receptor coilin and this complex then enters by endocytosis into enterocytes.
• Inside the enterocyte cobalamin binds to other carriers and excreted into the plasma.
• 75-80% is bound to apocrine and goes to hepatocytes.
• he cells of other organs enter only vitamin B₁₂ bound to transcobalamin II after binding to specific receptors through endocytosis.
• The cell cobalamin is converted to active metabolites and adenosyl cobalamin methyl cobalamin, which serve as cofactors of enzymes.
• The daily recommended dose for adults : 3 mg.
• Minimal in infants: approximately 0.1 to 0.3 mg.

Function:-

• Hemopoiesis; development of the central nervous system in childhood; cofactor of two metabolic reactions: conversion of homocysteine to methionine by methionine synthase (failure of this reaction leads to the accumulation of homocysteine); conversion methylmalonic-CoA to succinyl-CoA action methylmalonic-CoA mutase.

Deficit:-

• Its deficiency is clinically manifested failure to thrive, macrocytic anemia and neurological symptoms.
• An adult is a stock (2-5 mg) of vitamin B₁₂ in the liver, which cover the need for a period of 5-10 years.
• Stocks, which creates the infant in utero, will be exhausted as early as 3-5 months.

• Among laboratory manifestations include mostly macrocytic anemia, elevated aminotransferases, hype homocystinuria and increased acid secretion methylmalonic acid plasma concentrations of homocysteine and methylmalonic acid excretion increased in the urine.
• Metabolic changes precede clinical manifestations.
• Pernicious anemia is an autoimmune disease that leads to atrophy of the gastric mucosa and by the lack of intrinsic factor.

Surplus:-

• Signs of excess were reported even after a high intake (5 mg) of the supplement.

Vitamin C:-

• L-ascorbic acid , also known as vitamin C is water soluble strongly reducing effects.
• Man cannot synthesize it, since it lacks L-gluconolactone oxidase activity, therefore it must receive in food.
• L-ascorbate is involved in the hydroxylation of collagen , the synthesis of carnitine , the metabolism of tyrosine , acts as an antioxidant, supports immune system, iron absorption, has an effect on beta-oxidation of fatty acids , increases the activity of microsomal enzymes, accelerates the detoxification of xenobiotics.
• Reducing the effects of ascorbic acid are due to its easy oxidation to dehydrin ascorbate:

Source:-

• Fruits, vegetables (including potatoes), liver. Average losses in cook foods are 30%.
• The daily recommended dose for adults : 100 mg .
• When the determination is considered, in addition to prevention of deficiency symptoms, as well as strengthening the immune system and prevention of degenerative diseases.
• Increased need for considerable physical exertion, psychological stress, alcohol abuse and drugs, some diseases (e g diabetes, renal insufficiency, infection).
• Intake of 150 mg / day is recommended for smokers.

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Deficit:-

• Ascorbic acid deficiency - scurvy (scurvy) - now appears only in extreme conditions.
• With a slight lack of preclinical manifestations we see in our country.
• Laboratory evaluation of the situation: the level of vitamin C in plasma.
• Clinical symptoms appear with values ≤ 10 µmol/L, an indicator of low intake of vitamin C are considered to values below 37 µmol/L.
• In terms of prevention of atherosclerosis and the tumors are regarded as desirable values ≥ 50 µmol / L.

Surplus:-

• Signs of excess food are not.
• Approximately 1% of the unused vitamin C is converted to oxalate, the risk of urinary calculi, but low in healthy subjects.
• The care the daily intake should not exceed 1000 mg.
• Very high doses (5 g) can cause diarrhea .
• At high ascorbate intake (about grams per day), most of the substance excreted in the urine.
• It can then interfere with many clinical biochemistry determination by routine chemical urinalysis.

• Respiration is the process in which organisms exchange gases between their body cells and the environment.
• Respiration may refer to any of the three elements of the process.
• First, respiration may refer to external respiration or the process of breathing also called ventilation. 
• Secondly, respiration may refer to internal respiration, which is the diffusion of gases between body fluids and tissues. 
• Finally, respiration may refer to the metabolic processes of converting the energy stored in biological molecules to usable energy in the form of ATP.
• This process may involve the consumption of oxygen and production of carbon dioxide, as seen in aerobic cellular respiration, or may not involve the consumption of oxygen, as in the case of anaerobic respiration.

3. Respiration:-

Introduction:-

• Respiration, process by which an organism exchanges gases with its environment.
• The term now refers to the overall process by which oxygen is abstracted from air and is transported to the cells for the oxidation of organic molecules while carbon dioxide (CO₂) and water, the products of oxidation, are returned to the environment.
• In single-celled organisms, gas exchange occurs directly between cell and environment, at the cell membrane.
• Organisms that utilize respiration to obtain energy are aerobic, or oxygen-dependent.
• Some organisms can live in the absence of oxygen and obtain energy from fuel molecules solely by glycolysis  these anaerobic processes are much less efficient, since the fuel molecules are merely converted to end products such as lactic acid and ethanol, with relatively little energy-rich ATP produced during these conversions.

There are two Kinds of respiration:-

Kinds of Respiration:-

Define Aerobic and Anaerobic respiration

Kinds of Respiration:-

• Aerobic respiration is a type of cellular respiration, which takes place in the presence of oxygen.
• This type of respiration is common in all plants and higher animals, including humans, mammals, and birds.
• Anaerobic respiration is a type of cellular respiration that takes place in the absence of oxygen and is common in all lower organisms such as bacteria and yeast.

Aerobic respiration:-

• It is a type of cellular respiration that takes place in the presence of oxygen to produce energy.
• It is a continuous process that takes place within the cells of animals and plants.
• This process can be explained with the help of the chemical equation:-

Glucose(C₆H₁₂O₆) + Oxygen(6O₂) → Carbon dioxide(6CO₂) + Water(6H₂O)+  Energy (ATP)

Anaerobic respiration:-

• It is a type of cellular respiration that takes place in the absence of oxygen to produce energy.
• The chemical equation for anaerobic respiration is

Glucose(C₆H₁₂O₆) → Alcohol 2(C₂H₅O H) + Carbon dioxide 2(CO₂) + Energy (ATP )

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Phases of Respiration in Organisms:-

• Respiration occurs in the cytosol and around the plasma membrane in prokaryotic cells.
• In eukaryotic cells, respiration takes place in the mitochondria, which is also considered as the powerhouse of the cells.
• This process is very much similar to internal combustion of the car engine, wherein organic compounds and oxygen go in, while water and carbon dioxide comes out.
• The energy that is liberated powers the automotive (or cell).
• The three phases of Respiration are:-

1. Glycolysis:-

• The molecules of glucose get converted into pyruvic acid which is oxidized to carbon dioxide and water, leaving two carbon molecules, known as acetyl-CoA.
• During the process of glycolysis, two molecules of ATP and NADH are produced.
• Pyruvate enters the inner matrix of mitochondria and undergoes oxidation in the Kerbs' cycle.

• Oxidative phosphorylation is the process in which ATP molecules are formed as a result of the transfer of electrons from NADH or FADH₂ to O₂ by a series of electron carriers.
• This process takes place within the mitochondria of a cell.

3. Citric Acid Cycle:-

• This is also known as the tricarboxylic acid cycle or Krebs's cycle.
• Two ATP molecules are produced in each phase of the citric acid cycle and it takes place within the mitochondrial matrix of a cell.
• The electrons generated in the Krebs's cycle move across the mitochondrial matrix.

Types of Respiration:-

• Respiration is the process of gas exchange between the air and an organism's cells.
• Three types of respiration include internal, external, and cellular respiration.
• External respiration is the breathing process. It involves inhalation and exhalation of gases.
• Internal respiration is involves gas exchange between the blood and body cells. 
• Cellular respiration is involves the conversion of food to energy. 
• Aerobic respiration is a cellular respiration that requires oxygen while anaerobic respiration does not.

External Respiration:-

• One method for obtaining oxygen from the environment is through external respiration or breathing.
• In animal organisms, the process of external respiration is performed in a number of different ways.
• Animals that lack specialized organs for respiration rely on diffusion across external tissue surfaces to obtain oxygen.
• Others either have organs specialized for gas exchange or have a complete respiratory system.
• In organisms such as nematodes gases and nutrients are exchanged with the external environment by diffusion across the surface of the animals body.
• Insects and spiders have respiratory organs called tracheae, while fish have gills as sites for gas exchange.
• Humans and other mammals have a respiratory system with specialized respiratory organs (lungs) and tissues.
• In the human body, oxygen is taken into the lungs by inhalation and carbon dioxide is expelled from the lungs by exhalation.
• External respiration in mammals encompasses the mechanical processes related to breathing.

Internal Respiration:-

• External respiratory processes explain how oxygen is obtained, but how does oxygen get to body cells?
• Internal respiration involves the transportation of gases between the blood and body tissues.
• Oxygen within the lungs diffuses across the thin epithelium of lung alveoli into surrounding capillaries containing oxygen depleted blood.
• At the same time, carbon dioxide diffuses in the opposite direction and is expelled.
• Oxygen rich blood is transported by the circulatory system from lung capillaries to body cells and tissues.
• While oxygen is being dropped off at cells, carbon dioxide is being picked up and transported from tissue cells to the lungs.

Cellular Respiration:-

• The oxygen obtained from internal respiration is used by cells in cellular respiration.
• In order to access the energy stored in the foods we eat, biological molecules composing foods (carbohydrates, proteins, etc,) must be broken down into forms that the body can utilize.
• This is accomplished through the digestive process where food is broken down and nutrients are absorbed into the blood.
• As blood is circulated throughout the body, nutrients are transported to body cells.
• In cellular respiration, glucose obtained from digestion is split into its constituent parts for the production of energy.
• Through a series of steps, glucose and oxygen are converted to carbon dioxide (CO₂), water (H₂O), and the high energy molecule adenosine triphosphate (ATP).
• Carbon dioxide and water formed in the process diffuse into the interstitial fluid surrounding cells.
• From there, CO₂ diffuses into blood plasma and red blood cells.
• ATP generated in the process provides the energy needed to perform normal cellular functions, such as macromolecule synthesis, muscle contraction, cilia and flagella movement, and cell division.

Difference between direct and indirect respiration Explanation:-

• Direct Respiration- there's an immediate exchange of gases between the carbon-di-oxide of body cells and atomic number 8 of water and there's no blood is required for the transport of gases.
• The exchange of gases happens on the principle of diffusion.
• It's found in animate thing organisms like aerobic microorganism e.g.

rhizopod an or metazoans like sponges, (e.g. Hydra)

• Indirect Respiration-In this kind of respiration there's no direct contact between the body cells and also the close air of water supply of atomic number 8 is thought as a metabolic process medium.
• This kind is found in a very larger or complicated style of animals.
• These organisms have some specialised organs like gills (most of the crustaceans molluscs), lungs ( some amphibians, snails, all reptiles, birds or mammals).
• In this, the transportation of atomic number 8 or carbon-di-oxide between the metabolic process organs or the body cells is caused by the blood of the vascular system.
• So, it's known as Indirect respiration Read more on Brainly.

Respiratory organ in man:-

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• The respiratory system consists of all the organs involved in breathing. These include the nose, pharynx, larynx, trachea, bronchi and lungs.
• The respiratory system does two very important things: it brings oxygen into our bodies, which we need for our cells to live and function properly; and it helps us get rid of carbon dioxide, which is a waste product of cellular function.
• The nose, pharynx, larynx, trachea and bronchi all work like a system of pipes through which the air is funnel led down into our lungs.
• There, in very small air sacs called alveoli, oxygen is brought into the bloodstream and carbon dioxide is pushed from the blood out into the air.

Lungs:-

• Their role is to take oxygen into the body, which we need for our cells to live and function properly, and to help us get rid of carbon dioxide, which is a waste product.

Structure:-� The lungs are paired, cone-shaped organs which take up most of the space in our chests, along with the heart.

• We each have two lungs, a left lung and a right lung.
• These are divided up into ‘lobes’, or big sections of tissue separated by ‘dividers.
• The right lung has three lobes but the left lung has only two, because the heart takes up some of the space in the left side of our chest.
• The lungs can also be divided up into even smaller portions, called ‘bronchopulmonary segments .These are pyramidal-shaped areas which are also separated from each other by membranes.
• There are about 10 of them in each lung.
• Each segment receives its own blood supply and air supply.

How they work:-� Air enters your lungs through a system of pipes called the bronchi.

• These pipes start from the bottom of the trachea as the left and right bronchi and branch many times throughout the lungs, until they eventually form little thin-walled air sacs or bubbles, known as the alveoli.
• The alveoli are where the important work of gas exchange takes place between the air and your blood.
• Covering each alveolus is a whole network of little blood vessel called capillaries, which are very small branches of the pulmonary arteries.
• It is important that the air in the alveoli and the blood in the capillaries are very close together, so that oxygen and carbon dioxide can move between them.
• So, when you breathe in, air comes down the trachea and through the bronchi into the alveoli.
• This fresh air has lots of oxygen in it, and some of this oxygen will travel across the walls of the alveoli into your bloodstream.

Blood supply:-

• The lungs are very vascular organs, meaning they receive a very large blood supply.
• This is because the pulmonary arteries, which supply the lungs, come directly from the right side of your heart.
• They carry blood which is low in oxygen and high in carbon dioxide into your lungs so that the carbon dioxide can be blown off, and more oxygen can be absorbed into the bloodstream.
• The newly oxygen-rich blood then travels back through the paired pulmonary veins into the left side of your heart.
• From there, it is pumped all around your body to supply oxygen to cells and organs.

Work of Breathing:-

Pleurae:-� The lungs are covered by smooth membranes that we call pleurae.

• The pleurae have two layers, a ‘visceral’ layer which sticks closely to the outside surface of your lungs, and a ‘parietal’ layer which lines the inside of your chest wall (ribcage).
• The pleurae are important because they help you breathe in and out smoothly, without any friction.
• They also make sure that when your ribcage expands on breathing in, your lungs expand as well to fill the extra space.

The Diaphragm and Intercostal Muscles:-�When you breathe in (inspiration), your muscles need to work to fill your lungs with air.

• The diaphragm, a large, sheet-like muscle which stretches across your chest under the ribcage, does much of this work.
• At rest, it is shaped like a dome curving up into your chest.
• When you breathe in, the diaphragm contracts and flattens out, expanding the space in your chest and drawing air into your lungs.
• Other muscles, including the muscles between your ribs also help by moving your ribcage in and out.
• Breathing out (expiration) does not normally require your muscles to work.
• This is because your lungs are very elastic, and when your muscles relax at the end of inspiration your lungs simply recoil back into their resting position, pushing the air out as they go.

Respiration in man:-

• Mechanism of respiration in man takes place in two phases, namely inspiration and expiration.
•  Inspiration is the process of inhaling air into the lungs.
• During inspiration, the muscles of diaphragm contract and the diaphragm moves downward.
• This results in the increase in the volume of the chest cavity, The air pressure inside the chest cavity decreases.
• The oxygenated air present outside the body being at high-pressure flow rapidly into the lungs.
• In the lungs, oxygenated air reaches the alveoli.

Mechanism of respiration in man:-

• Alveoli are thin walled and are surrounded by a network of blood capillaries.
• The oxygen passes through the walls of the alveoli into the blood present in blood capillaries.
• The oxygen is then supplied to all the tissues of the body.
• From the tissues, the waste product, carbon dioxide is absorbed by blood and carried to the alveoli of lungs for expiration. 
• Expiration is the process of exhaling air from lungs.
• This results in the decrease in the volume of the chest cavity he air pressure inside the chest cavity increases.
• This pushes out carbon dioxide outside the body.

Transport of Oxygen and Carbon dioxide:-

• Once the oxygen diffuses across the alveoli, it enters the bloodstream and is transported to the tissues where it is unloaded, and carbon dioxide diffuses out of the blood and into the alveoli to be expelled from the body.
• Although gas exchange is a continuous process, the oxygen and carbon dioxide are transported by different mechanisms.

Transport of Oxygen in the Blood:-

• Although oxygen dissolves in blood, only a small amount of oxygen is transported this way.
• Only 1.5 percent of oxygen in the blood is dissolved directly into the blood itself.
• Most oxygen—98.5 percent—is bound to a protein called hemoglobin and carried to the tissues.

Transport of Oxygen and Carbon dioxide:-

Blood:-

Hemoglobin:-

• Hemoglobin is a protein molecule found in red blood cells (erythrocytes) made of four subunits: two alpha subunits and two beta subunits.
• Each subunit surrounds a central heme group that contains iron and binds one oxygen molecule, allowing each hemoglobin molecule to bind four oxygen molecules.
• Molecules with more oxygen bound to the heme groups are brighter red.
• As a result, oxygenated arterial blood where the Hb is carrying four oxygen molecules is bright red, while venous blood that is deoxygenated is darker red.

• It is easier to bind a second and third oxygen molecule to Hb than the first molecule.
• This is because the hemoglobin molecule changes its shape,, as oxygen binds.
• The fourth oxygen is then more difficult to bind.
• The binding of oxygen to hemoglobin can be plotted as a function of the partial pressure of oxygen in the blood (x-axis) versus the relative Hb-oxygen saturation (y-axis).
• The resulting graph—an oxygen dissociation curve—is sigmoidal, or S-shaped.
• As the partial pressure of oxygen increases, the hemoglobin becomes increasingly saturated with oxygen.

• The kidneys are responsible for removing excess H+ ions from the blood.
• If the kidneys fail, what would happen to blood pH and to hemoglobin affinity for oxygen?

Factors That Affect Oxygen Binding:-

• The oxygen-carrying capacity of hemoglobin determines how much oxygen is carried in the blood.
• In addition to P_O2, other environmental factors and diseases can affect oxygen carrying capacity and delivery.
• Carbon dioxide levels, blood pH, and body temperature affect oxygen-carrying capacity.
• When carbon dioxide is in the blood, it reacts with water to form bicarbonate (HCO⁻₃) and hydrogen ions (H⁺).
• As the level of carbon dioxide in the blood increases, more H⁺ is produced and the pH decreases.
• This increase in carbon dioxide and subsequent decrease in pH reduce the affinity of hemoglobin for oxygen.

​

• The oxygen dissociates from the Hb molecule, shifting the oxygen dissociation curve to the right.
• Therefore, more oxygen is needed to reach the same hemoglobin saturation level as when the pH was higher.
• A similar shift in the curve also results from an increase in body temperature.
• Increased temperature, such as from increased activity of skeletal muscle, causes the affinity of hemoglobin for oxygen to be reduced.
• Diseases like sickle cell anemia and thalassemia decrease the blood’s ability to deliver oxygen to tissues and its oxygen-carrying capacity.
• In sickle cell anemia, the shape of the red blood cell is crescent-shaped, elongated, and stiffened, reducing its ability to deliver oxygen.
• In this form, red blood cells cannot pass through the capillaries.
• This is painful when it occurs.
• Thalassemia is a rare genetic disease caused by a defect in either the alpha or the beta subunit of Hb.
• Patients with thalassemia produce a high number of red blood cells, but these cells have lower-than-normal levels of hemoglobin.
• Therefore, the oxygen-carrying capacity is diminished.

Transport of Carbon Dioxide in the Blood:-

• Carbon dioxide molecules are transported in the blood from body tissues to the lungs by one of three methods:
• Dissolution directly into the blood, binding to hemoglobin, or carried as a bicarbonate ion.
• Several properties of carbon dioxide in the blood affect its transport.
• First, carbon dioxide is more soluble in blood than oxygen.
• About 5 to 7 percent of all carbon dioxide is dissolved in the plasma.
• Second, carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin.
• This form transports about 10 percent of the carbon dioxide.
• When carbon dioxide binds to hemoglobin, a molecule called carbaminohemoglobin is formed.
• Binding of carbon dioxide to hemoglobin is reversible.
• Therefore, when it reaches the lungs, the carbon dioxide can freely dissociate from the hemoglobin and be expelled from the body.
• Third, the majority of carbon dioxide molecules (85 percent) are carried as part of the bicarbonate buffer system.

​

• In this system, carbon dioxide diffuses into the red blood cells.
• Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H₂CO₃).
• Carbonic acid is an unstable intermediate molecule that immediately dissociates into  (HCO⁻₃)  and hydrogen (H⁺) ions.
• Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood down its concentration gradient.
• It also results in the production of H⁺ ions. If too much H⁺ is produced, it can alter blood pH .
• However, hemoglobin binds to the free H⁺ ions and thus limits shifts in pH .
• The newly synthesized bicarbonate ion is transported out of the red blood cell into the liquid component of the blood in exchange for a chloride ion (Cl^–); this is called the
• When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion.
• The H⁺ ion dissociates from the hemoglobin and binds to the bicarbonate ion.
• This produces the carbonic acid intermediate, which is converted back into carbon dioxide through the enzymatic action of CA.
• The carbon dioxide produced is expelled through the lungs during exhalation.

• The benefit of the bicarbonate buffer system is that carbon dioxide is “soaked up” into the blood with little change to the pH of the system.
• This is important because it takes only a small change in the overall pH of the body for severe injury or death to result.
• The presence of this bicarbonate buffer system also allows for people to travel and live at high altitudes:
• When the partial pressure of oxygen and carbon dioxide change at high altitudes, the bicarbonate buffer system adjusts to regulate carbon dioxide while maintaining the correct pH in the body.

Carbon Monoxide Poisoning:-

• While carbon dioxide can readily associate and dissociate from hemoglobin, other molecules such as carbon monoxide (CO) cannot.
• Carbon monoxide has a greater affinity for hemoglobin than oxygen.
• Therefore, when carbon monoxide is present, it binds to hemoglobin preferentially over oxygen.
• As a result, oxygen cannot bind to hemoglobin, so very little oxygen is transported through the body.
• Carbon monoxide is a colorless, odorless gas and is therefore difficult to detect.
• It is produced by gas-powered vehicles and tools.
• Carbon monoxide can cause headaches, confusion, and nausea; long-term exposure can cause brain damage or death.
• Administering 100 percent (pure) oxygen is the usual treatment for carbon monoxide poisoning.
• Administration of pure oxygen speeds up the separation of carbon monoxide from hemoglobin.

UNIT-II

1. Excretion:- 

• Excretion is a process by which metabolic waste is eliminated from an organism.
• In vertebrates this is primarily carried out by the lungs, kidneys and skin.
• This is in contrast with secretion, where the substance may have specific tasks after leaving the cell.
• Excretion is an essential process in all forms of life . For example, in mammals urine is expelled through the urethra, which is part of the excretory system.
• In unicellular organisms, waste products are discharged directly through the surface of the cell.
• During life activities such as cellular respiration, several chemical reactions take place in the body.
• These are known as metabolism.
• These chemical reactions produce waste products such as carbon dioxide, water, salts, urea and uric acid.
• Accumulation of these wastes beyond a level inside the body is harmful to the body.

• In animals ,them ani excretory productsar carbondioxide, ammonia , urea  uric,acid 

guanine and creatine.

• The liver and kidneys clear many substances from the blood and the cleared substances are then excreted from the body in the urine and feces.
• Aquatic animals usually excrete ammonia directly into the external environment, as this compound has high solubility and there is ample water available for dilution.
• In terrestrial animals ammonia-like compounds are converted into other nitrogenous materials as there is less water in the environment and ammonia itself is toxic.

• Birds excrete their nitrogenous wastes as uric acid in the form of a paste.
• Although this process is metabolically more expensive, it allow smoreefficient water retention and it can be stored more easily in the egg.
• In insects, a system involving Malpighian tubules is utilized to excrete metabolic waste.
• Metabolic waste diffuses or is actively transported into the tubule, which transports the wastes to the intestines.
• The metabolic waste is then released from the body along with fecal matter.
• The excreted material may be called ejecta.

Structure of kidney:-

Structure:-

• Kidneys are bean-shaped organs, about 11 cm long, 6 cm wide, 3 cm thick and weigh 150 g.
• They are embedded in, and held in position by, a mass of adipose tissue.
• Each kidney is enclosed by a thin tough fibrous connective tissue called renal capsule that protects it from infections and injuries.
• Around the capsule there is a layer of fat which is further enclosed by another layer of fibrous membrane known as renal fascia.
• The bean shaped kidney have outer convex surface and inner concave surface.

Location:- The kidneys lie on the posterior abdominal wall, one on each side of the vertebral column, behind the peritoneum and below the diaphragm.

Position:- It is situated at the level of T12-L3.

• The right kidney is usually slightly lower than the left, probably because of the considerable space occupied by the liver.

Anatomy of kidney:-

• Longitudinal section of the kidney shows following parts.

Capsule:- It is an outermost covering composed of fibrous tissue surrounding the kidney.

Cortex:- It is a reddish-brown layer of tissue immediately below the capsule and outside the renal It consists of renal corpuscles and convoluted tubules.

Medulla:- It is the innermost layer, consisting of conical areas called the renal pyramids separated by renal columns.

• There are 8-18 renal pyramids in each kidney.
• The apex of each pyramid is called a renal papilla, and each papilla projects into a small depression, called a minor calyx. 
• Several minor calyces unite to form a major calyx. 
• In turn, the major calyces join to form a funnel shaped structure called renal pelvis that collects urine and leads to ureter.

Nephron:-

Definition:-

• A nephron is the basic unit of structure in the kidney.
• A nephron is used separate to water, ions and small molecules from the blood, filter out wastes and toxins, and return needed molecules to the blood.
• The nephron functions through ultrafiltration.
• Ultrafiltration occurs when blood pressure forces water and other small molecules through tiny gaps in capillary walls.
• This substance, lacking the blood cells and large molecules in the bloodstream, is known as an ultrafiltrate.
• The ultrafiltrate travels through the various loops of the nephron, where water and important molecules are removed, and into a collecting duct which drains into the bladder.
• The glomerulus is the specialized configuration of capillaries within the nephron that make kidneys possible.

• Vertebrates are the only group to have developed kidneys, which is mostly used to conserve water in terrestrial environments.
• Fish and other primitive vertebrates excrete ammonia as a byproduct of protein reactions.
• Ammonia is toxic in the bloodstream, and must be removed.
• Reptiles and birds excrete uric acid, which is a more concentrated form of ammonia.
• Mammals have even more derived nephrons, which contain an extended loop, called the loop of Henle.
• Mammals produce urea from ammonia, and concentrate the urea in the urine to a high extent.
• This promotes the extraction of water from the ultrafiltrate, and allows mammals to live in some of the driest environments on Earth.
• A camel, for instance, will continually filter most of the water from its blood, recollect a large majority of that water, and reuse it continually.

Structure of Nephron:-

• Diagram (left) of a long juxtamedullary nephron and (right) of a short cortical nephron.
• The left nephron is labelled with six named nephron segments.
• Also labelled is the collecting duct, mislabeled the "collection duct"; it is the last part of the nephron

Structure of Nephron:-

• The picture below is of a general nephron.
• This nephron contains a loop of Henle, so it is a mammalian nephron.
• While the loop of the nephron is special to mammals, the rest of the structure is seen in all vertebrate animals.
• The glomerulus is the net of capillaries inside of the glomerular capsule.
• While the picture shows the glomerular capsule and the rest of the renal tubule look to be the same in the graphic below, they are in fact composed of a wide variety of cell types, intended to extract and retain certain chemicals within the tubules.

• Each nephron consists of one main interlobular artery feeding a single renal tubule.
• Each kidney in a vertebrate has hundreds to millions of nephrons, each of which produces urine and sends it to the bladder.
• The cells in each nephron are arranged so that the most concentrated cells are at the bottom of the nephron, while the cells at the top are less concentrated.
• The cells near the exit of the nephron are the most concentrated, and therefore extract as much water as possible from the ultrafiltrate before it is sent to the bladder.

Function of Nephron:-

• A nephron is responsible for removing waste products, stray ions, and excess water from the blood.
• The blood travels through the glomerulus, which is surrounded by the glomerular capsule.
• As the heart pumps the blood, the pressure created pushes small molecules through the capillaries and into the glomerular capsule.
• This is the, more physical function of the nephron.
• Next, the ultrafiltrate must travel through a winding series of tubules.
• The cells in each part of the tube have different molecules that they like to absorb.
• Molecules to be excreted remain in the tubule, while water, glucose and other beneficial molecules work their way back into the bloodstream.
• As the ultrafiltrate travels down the tubules, the cells become more an more hypertonic 

compared to the ultrafiltrate.

• This causes a maximum amount of water to be extracted from the ultrafiltrate before it exits the nephron.
• The blood surrounding the nephron returns to the body via the interlobular vein, free of toxins and excess substances.
• The ultrafiltrate is now urine, and moves via the collecting duct to the bladder, where it will be stored.

Mechanisms of Urine Formation:-

• Urine formation begins with the delivery of blood to the glomerulus followed by its filtration past the glomerular barrier.
• The filtered portion of plasma continues through the nephron whereas the unfiltered portion passes into the peritubular capillaries.
• As the filtered portion travels through the nephron, water and certain solutes are resorbed back into the peritubular capillaries whilst other solutes are secreted from the peritubular capillaries into the nephron.
• Whatever fluid is remains at the end of the nephron is discarded as urine.
• Here we discuss the basic mechanistic that which are involved in formation of urine.

Functional organization of the glomerulonephritis unit:-

• Blood enters the glomerulus via the afferent arteriole and leaves via the efferent arteriole to enter the peritubular capillaries that surround the nephron.
• The glomerular filtrate then enters the nephron and travels through it.
• At the different stages of the nephron the filtrate is modified by mechanisms which specifically resorb or secrete small molecules including water, into or out of the filtrate.
• These molecules enter the interstitial fluid where they non-specifically enter and exit the peritubular capillaries.
• Whatever fluid and molecules remain in the nephron at its end are excreted as urine.

Ultra-filtration (kidney):-

• Blood is filtered in the kidney underhighpressure,aprocesscalled ultrafiltration.  
• Filtration is a way of separating a mixture of chemicals based on the size of the particles and this is exactly what happens to the blood in the kidney.  
• Red blood cells, white blood cells and platelets are all too large to cross the filtration barrier.  
• Blood plasma is filtered from the blood forming aliquidcalled glomerularfiltrate.  
• The kidneys produce about 180 liters of glomerular filtrate per day.

• Ultrafiltration happens in the glomerulus and the glomerular filtrate (GF) passes into the Bowmans capsule.  
• The high pressure is generated by the blood vessel that takes blood into the glomerulus being much wider than the blood vessel that takes blood out of the glomerulus.
• The plasma of blood is squeezed out of the very leaky capillaries in the glomerulus and into the first part of the nephron.

• In renal physiology, ultrafiltration occurs at the barrier between the blood and the filtrate in the glomerular capsule in the kidneys.
• As in nonbiological examples of ultrafiltration, pressure and concentration gradients lead to a separation through a semipermeable membrane. 
• The Bowman's capsule contains a dense capillary network called the glomerulus.
• Blood flows into these capillaries through the afferent arterioles and leaves through the efferent arterioles.
• Thehighhydrostaticpressureforcessmallmoleculeinthe tubularfluid such as water, glucose, amino acids, sodiumchloride and urea through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman's capsule and into the renal tubules.

Tubular Re-absorption:-

• In renal physiology,  tubular reabsorption is the process by which the nephron removes water and solutes from the tubular fluid and returns them to the circulating blood.
• It is called reabsorption both because these substances have already been absorbed once and because the body is reclaiming them from a post glomerular fluid stream that is well on its way to becoming urine .
• Substances are reabsorbed from the tubule into the peritubular capillaries.
• Thus, the glomerular filtrate becomes more concentrated, which is one of the steps in forming urine.
• Reabsorptionallowsmanyuseful solutes (primarily glucose and aminoacids), salts and water  that have passed through Bowman's capsule, to return to the circulation.
• These solutes are reabsorbed isotopically, in that the osmotic potential of the fluid leaving the proximal convoluted tubule is the same as that of the initial glomerular filtrate.
• However, glucose, amino acids, inorganic phosphate, and some other solutes are reabsorbed via secondary active transport through cotransport channels driven by the sodium gradient.

Renin–angiotensin system:

• The kidneys sense low blood pressure.
• Release renin into the blood.
• Renin causes production of angiotensin I.
• Angiotensin-converting enzyme (ACE) converts angiotensin I to angiotensin II.
• Angiotensin II stimulates the release of aldosterone, ADH, and thirst.
• Aldosterone causes kidneys to reabsorb sodium; ADH increases the uptake of water.
• Water follows sodium.
• As blood volume increases, pressure also increases.

Counter-Current Mechanisms:-

• The mechanisms shown here are traditionally called the 'counter-current multiplier' and the 'counter-current exchanger’.
• The first takes place in the region of the nephron called Henle's loop; the second occurs in a region of the peritubular capillary bed called the 'vasa recta’.
• Both are involved in establishing an osmotic gradient throughout this region.

Henle's Loop:-

• The portion of the nephron called the 'Henle's loop' is shown in the right half of the illustration.
• It consists of a descending limb that has a down arrow in it and an ascending limb with an up arrow in it.
• The ascending limb has a thick and a thin segment.
• The dots represent various solutes that become more concentrated in both limbs toward the bottom of the loop.
• The thick walls of the ascending limb indicates that this region is impermeable to water.

Vasa Recta:-

• This capillary bed is shown in red at the left of the illustration.
• It also consists of a descending limb and an ascending limb identified by the arrows in each.
• Again, the dots represent various solutes that are more concentrated at the bottom of the loop.

Counter-Currents:-

• Counter-currents exist when fluids flow in opposite directions in parallel and adjacent tubes.
• The two limbs of Henle's loop are a counter-current.
• The two limbs of the vasa recta are also a counter-current.
• It is apparent that these two sets of tubes are parallel and adjacent.
• Not apparent in the mind map is the fact that the descending limb of Henle is also counter-current with the ascending limb of the vasa recta; the same is true of the ascending limb of Henle and the descending vasa recta.

Counter-Current Exchanger:-

• Examination of both limbs of the vasa recta shows the concentration of solutes (number of dots) is the same at any horizontal level.
• However, imagine the fluid flowing through the vasa recta for a short distance then stopping.
• Now compare the concentration of solutes at any level and they will not be the same.
• At any level the solute concentration in the descending limb will be less than in the ascending limb! But, because both limbs are freely permeable, sodium chloride will diffuse from the ascending into the descending while water will diffuse from the descending to the ascending...see block arrows.
• When equilibrium is reached both limbs will, once again, have the same concentration of water and solutes.
• Water is exchanged for sodium chloride...the counter-current exchange mechanism.

​

Counter-Current Multiplier:-

• The above described counter-current exchanger would not exist if there were not some mechanism to initially make the vasa recta more concentrated at the bottom of the loop.
• This is accomplished by the loop of Henle.
• The ascending limb of Henle and the early distal tubule are impermeable to water as indicated by their thick wall.
• These regions actively transports sodium chloride (NaCl) out of the filtrate and into the surroundings.
• The NaCl diffuses into the descending limb of the vasa recta...block arrow.
• Any that might diffuse into the descending limb of Henle will only get pumped back out when it enters the ascending limb so this is not shown in the mind map.
• It will not diffuse into the ascending vasa recta because that fluid is already highly concentrated.
• This is the mechanism that 'multiplies' the concentration of NaCl in the descending vasa recta making the counter-current exchanger possible!

Osmosis:-

• Both blood and filtrate descending into their respective loops have low solute concentrations.
• Both flow beside upcoming columns having higher solute concentrations.
• As they move past one another, water from the down-flowing fluid columns will diffuse into the more concentrated up-flowing columns.
• However, only the up-flowing vasa recta is permeable to water meaning all is returned to the blood and none to the filtrate...see both block arrows.
• This also insures that a high solute concentration will be maintained at the bottom of both loops.

Urea:-

• Urea passively diffuses among and between the lower portions of both the blood and the filtrate loops as indicated by the large block arrow spanning this region.
• The result is that half the urea is excreted and half kept in the body.

2. Cardiovascular System:-

Introduction:-

• The cardiovascular system is sometimes called the blood-vascular, or simply the circulatory, system.
• It consists of the heart, which is a muscular pumping device, and a closed system of vessels called arteries, veins, and capillaries.
• As the name implies, blood contained in the circulatory system is pumped by the heart around a closed circle of vessels as it passes again and again through the various "circulations" of the body.
• As in the adult, survival of the developing embryo depends on the circulation of blood to maintain homeostasis and a favorable cellular environment.
• In response to this need, the cardiovascular system makes its appearance early in development and reaches a functional state long before any other major organ system.

• Incredible as it seems, the primitive heart begins to beat regularly early in the fourth week following fertilization.
• The vital role of the cardiovascular system in maintaining homeostasis depends on the continuous and controlled movement of blood through the thousands of miles of capillaries that permeate every tissue and reach every cell in the body.
• It is in the microscopic capillaries that blood performs its ultimate transport function.
• Nutrients and other essential materials pass from capillary blood into fluids surrounding the cells as waste products are removed.
• Numerous control mechanisms help to regulate and integrate the diverse functions and component parts of the cardiovascular system in order to supply blood to specific body are as according to need.
• These mechanisms ensure a constant internal environment surrounding each body cell regardless of differing demands for nutrients or production of waste products.

• The cardiovascular system can be thought of as the transport system of the body.
• This system has three main components: the heart, the blood vessel and the blood itself.
• The heart is the system’s pump and the blood vessels are like the delivery routes.
• Blood can be thought of as a fluid which contains the oxygen and nutrients the body needs and carries the wastes which need to be removed.
• The following information describes the structure and function of the heart and the cardiovascular system as a whole.

• Blood is a red colour pigment that circulates in the body.
• It contains plasma, red blood cells, white blood cells, and platelets.
• It performs various functions in the body.
• Let us study in detail about the composition and function of blood, its components.

Composition and Functions of Blood:-

Blood:-

• Blood is a connective tissue that helps in the transportation of substances, protects against diseases and regulates the temperature of the body.
• Do you know why the colour of blood is red?
• It is red in colour due to a red pigment called hemoglobin present in its red cells.
• The components of Blood are Plasma, Red blood corpuscles (Red blood cells or RBCs), White blood corpuscles (White blood cells or WBCs) and platelets.
• First, we will study about Plasma.
• Plasma is a liquid also known as the fluid matrix and consists of three types of cells that keep floating in it namely red blood cells, white blood cells, and platelets.

Functions:-

• Blood has three main functions in the human body. i.e Transport of substances from one part of the body to the other like respiratory gases, waste products, enzymes , etc, protection against diseases and regulation of body temperature.
• Blood regulates body temperature.
• It carries oxygen from lungs to different parts of the body.
• It carries carbon dioxide from the body cells to the lungs for breathing out.
• It carries digested food from the small intestine to all parts of the body.
• It carries hormones from the endocrine glands to different organs of the body.
• It carries waste product urea from the liver to the kidneys for excretion.
• Defends against infection.
• On average, a healthy man has about 5 liter of blood in the body, while a woman has about 500 ml less than man.
•  So, total blood is about 60-80 ml/kg of body weight.

Plasma:-

• The fluid or liquid part of blood is called plasma.
• It is a colorless liquid that contains 90% water, protein, and inorganic salts.
• Plasma also contains some traces of other substances like amino acids, organic acids, vitamins, pigments and enzymes.
• It carries these dissolved substances from one part to another part in the body.
• The protein in plasma includes antibodies to assist in the body’s defense system against disease and infection.

Red Blood Corpuscles (RBC):-

• RBC is also known as erythrocytes.
• They are disc-shaped cells concave in the middle and visible under a microscope.

Functions:-

• Hemoglobin in RBC picks up oxygen in the lung tissues by forming a chemical compound with it.
• This oxygen is carried to the tissues where it is used in the chemical reactions to produce energy.
• It then combines with carbon dioxide which is produced in these reactions and returns to the lungs with the heart where the cycle starts again.

• RBC carries oxygen from the lungs to all the cells of the body.
• They have no nucleus and contain a pigment called hemoglobin which is made up of an iron-containing pigment known as harem and a protein called globin.
• RBCs are produced in the spleen and the bone marrow and live for about four months because they lack a nucleus.
• So, when we donate blood to save the life of a person, then the loss of blood from our body is recovered within a day because red blood cells are made very fast in the bone marrow.
• The life of the RBC is about 100-120 days.

.

White Blood Corpuscles (WBC):-

• WBC is also known as leukocytes.
• They fight with infection and protect us from diseases because they eat up the germs which cause diseases.
• That is why they are also known as ‘soldiers’ of the body’s defense system.
• They are round or irregular, semi-transparent cells containing a nucleus and visible under a microscope.
• They are a little larger than RBC.
• Some White blood cells make chemicals called ‘antibodies’ to fight against infection i.e why they provide immunity in our body.
• WBC in the blood is much smaller in number than red blood cells.

Functions:-

• Broadly, WBC acts as a defense system in the body.
• There are several varieties of WBC performing specific functions such as, Neutrophils (65 to 70% of the total WBC) attack the invading bacteria and engulf them. 
• Lymphocytes (25% of WBC) produces antibodies which protect the body against the antigen and thus provide immunity against infection.
• Basophils secrete anticoagulant called heparin which prevents clot within the blood cells. 
• Eosinophils and monocytes also assist in the defense mechanism of the body by becoming active against specific antigens.

Blood platelets:-

• Blood Platelets are also known as thrombocytes.
• They are tiny, circular or oval colorless cells formed in the bone marrow.
• They lack a nucleus and help in the coagulation of blood (clotting of blood) in a cut or wound, due to which bleeding stops.
• All the blood cells are made in the bone marrow from the cells called stem cells. 
• Blood clotting is a body’s defense system to combat bleeding.
• Plasma contains soluble protein fibrinogen of the blood which produces the insoluble protein called fibrin essential for blood coagulation which is formed in the liver.

Types of heart in vertebrates :-

Neurogenic hearts:-

Myogenic heart:-

Types of heart in vertebrates :-

Neurogenic hearts:-

• In animals with open circulatory system the heart is usually tubular.
• It has lateral openings which get closed when heart contracts and opens when heart relaxes.
• When heart relaxes vacuum is created to suck blood in the heart.
• Hence these hearts are known as suction pumps
• In most of the suction pump hearts the beating rhythm is set through nerve impulses.
• Such hearts are known as Neurogenic hearts.

Myogenic heart:-

• In some invertebrates and all vertebrates the heart is myogenic.
• In them the setting of the rhythm is by specialized cells.
• These cells are highly specialized for generating and conducting the impulse.
• In some animals they can be distinguished histologically from the other heart muscles

• In higher animals with closed circulatory system 2, 3 or 4 chambered hearts are seen with muscular ventricles which pumps the blood in the body with pressure and hence heart are known as pressure pumps.
• In pressure pump heart the rhythm is set in specialized muscle cells within the heart.
• They are known as Myogenic hearts.
• Most of the embryonic hearts are myogenic which later on may be become myogenic or neurogenic .

• The peacemaking regions are different from animal to animal.
• In Teleost cells of floor of atrium and auricula ventricular junction act as pacemaker.
• In elasmobranch fishes sinus Venuses, auricula ventricular junction and truncus arteriosus act as pacemaker.
• In amphibians and reptiles sinus venous us act as pacemakers.
• In mammals and birds sinus-atrial and auricula ventricular nodes act as pacemakers.
• In invertebrates the pace making area is wondering i.e. changing place.

• In birds and mammals as mentioned above peacemaking impulse arises in sinus-atrial node.
• It is a small mass in right atrium.
• It is situated near entrance of vein.
• Atrio-ventricular node is situated near auricula ventricular junction from which the impulse is carried to ventricle by specialized conducting muscles forming Auricula ventricular bundle of ‘His’ i.e. bundle of God.
• In birds bundle of His forms a network in atria.

• S.A. node is known to be true pacemaker.
• If it is surgically manipulated or given temperature, chemical or electrical stimuli, it affects cardiac activity, thus the wave of heart action starts from this point.
• The wave is picked up by A.V. node situated in right atrium near AV septum and then spreads into ventricle through the branches of auricular- ventricular bundles which forms a network in ventricle.

• In birds network is present in right and left atria as well.
• AV bundle tissue is highly specialized in conductance and hence spreads the impulse very fast.

• In myogenic heart in fact all cells have ability to set the rhythm. But certain cells are more specialized.
• The difference in them and other cells is they are highly unstable and have changing electrical potential.
• These cells are known as pacemaker cells.
• According to Kallikak and Miller heart have 3 type of cells

1) Pacemaker muscle cell. 2) Conductive muscle cell. 3) Contracting muscle cells.

• Pacemaker cells initially have inside negative as compared to outside and have a charge or potential of about –55 mV.
• This charge is unstable there is a slow leakage up to –30 mV which is known as slow depolarization.
• This is followed by rapid depolarization up to +10 mV.
• This depolarization causes contraction of muscles.
• The depolarization is followed by repolarization which causes relaxation or diastole

• These changes in the form of depolarization and repolarization spread in the heart muscle through conducting cells causing rhythmic contraction and relaxation of heart.
• This way the charges on pacemaker cells keep on changing constantly.

Structure and working of human Heart:-

• The human heart is a four-chambered muscular organ, shaped and sized roughly like a man's closed fist with two-thirds of the mass to the left of midline.
• The heart is enclosed in a pericardial sac that is lined with the parietal layers of a serous membrane.
• The visceral layer of the serous membrane forms the epicardium.

Layers of the Heart Wall:-

• Three layers of tissue form the heart wall.
• The outer layer of the heart wall is the epicardium, the middle layer is the myocardium, and the inner layer is the endocardium.

Chambers of the Heart:-

• The internal cavity of the heart is divided into four chambers:
• Right atrium
• Right ventricle
• Left atrium
• Left ventricle
• The two atria are thin-walled chambers that receive blood from the veins.
• The two ventricles are thick-walled chambers that forcefully pump blood out of the heart.
• Differences in thickness of the heart chamber walls are due to variations in the amount of myocardium present, which reflects the amount of force each chamber is required to generate.
• The right atrium receives deoxygenated blood from systemic veins; the left atrium receives oxygenated blood from the pulmonary veins.

Valves of the Heart:-

• Pumps need a set of valves to keep the fluid flowing in one direction and the heart is no exception.
• The heart has two types of valves that keep the blood flowing in the correct direction.
• The valves between the atria and ventricles are called atrioventricular valves, while those at the bases of the large vessels leaving the ventricles are called semilunar valves.
• The right atrioventricular valve is the tricuspid valve.
• The left atrioventricular valve is the bicuspid, or mitral, valve.
• The valve between the right ventricle and pulmonary trunk is the pulmonary semilunar valve.
• The valve between the left ventricle and the aorta is the aortic semilunar valve.
• When the ventricles contract, atrioventricular valves close to prevent blood from flowing back into the atria.
• When the ventricles relax, semilunar valves close to prevent blood from flowing back into the ventricles.
• Pathway of Blood through the Heart

Blood Supply to the Myocardium:-

• The myocardium of the heart wall is a working muscle that needs a continuous supply of oxygen and nutrients to function efficiently.
• For this reason, cardiac muscle has an extensive network of blood vessels to bring oxygen to the contracting cells and to remove waste products.
• The right and left coronary arteries, branches of the ascending aorta, supply blood to the walls of the myocardium.
• After blood passes through the capillaries in the myocardium, it enters a system of cardiac veins.
• Most of the cardiac veins drain into the coronary sinus, which opens into the right atrium.

• While it is convenient to describe the flow of blood through the right side of the heart and then through the left side, it is important to realize that both atria and ventricles contract at the same time.
• The heart works as two pumps, one on the right and one on the left, working simultaneously.
• Blood flows from the right atrium to the right ventricle, and then is pumped to the lungs to receive oxygen.
• From the lungs, the blood flows to the left atrium, then to the left ventricle.
• From there it is pumped to the systemic circulation.

Origin and Conduction of Cardiac Impulse:-

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Origin and conduction of cardiac impulse:-

• The heart is an electrically controlled muscular pump which sucks and pumps blood.
• The electrical signals which control the heart are generated within the heart itself.
• The heart is therefore capable of beating rhythmically in the absence of external stimuli; this is called auto rhythmicity.
• The SA Node
• Excitation of the heart arises in the pacemaker cells in the sine-atrial node.
• These cells initiate the heart beat.
• The SA node is located in the upper Right Atrium, close to where the Superior Vena Cava enters the right atrium.
• The SA node sets the pace for the entire heart; a heart under SA node control is said to be in “Sinus Rhythm”.
• Pacemaker cells produce excitation via depolarization of their cell membrane.
• Early depolarization is slow, and occurs via slow Na+ influx and a reduction in K+ efflux.
• Once these two ionic measures produce a minimum potential, they activate voltage-gated Ca+ channels.
• This causes rapid depolarization and the firing of an action potential from the node.
• After firing of an action potential, pacemaker cells repolarize slowly via K+ efflux.

Atrial depolarization:-

• Excitation is carried from the SA node through the atria via Gap Junctions between cells.
• This wave of depolarization is responsible for causing the Atria to contract.
• The AV node
• This node is the point of electrical communication between the atria and the ventricles.
• It has slow conduction velocity; this allows the atria time to contract before the signal reaches the ventricles and causes them to contract.
• Ventricular Conduction
• The Bundles of His and their branches, along with the Purkinje fibers, allow rapid spread of action potential to the ventricles.
• The ventricular muscles have cell-to-cell conduction, but their action potential is considerably different from that of the pacemaker cells.
• The resting membrane potential remains at -90 until the cell is excited.
• The rising phase of the action potential is caused by FAST Na+ influx; this rapidly reverses the membrane potential.
• The membrane potential is then maintained by Ca+ influx for a few hundred milliseconds.
• Repolarization is caused by inactivation of Ca+ channels and activation of K+ channels.

Regulation of Heart Rate:-

• Heart rate is driven by the SA node, and is mainly influenced by the Autonomic Nervous System.
• Parasympathetic stimulation decreases the heart rate, while sympathetic stimulation increases the heart rate.
• Normal resting heart rate is the result of continuous valgus nerve influence – known as Vagal tone.
• This reduces the Intrinsic heart rate from around 100bpm to around 70bpm.
• Resting heart rate is considered to be normal between 60 and 100bpm.

Parasympathetic Supply of the Heart:-

• The Vigus nerve supplies parasympathetic stimulation to the SA node and AV node.
• Vagal stimulation slows heart rate and increases AV nodal delay (widens QRS complex).
• It also hyperpolarizes pacemaker cells.
• The neurotransmitter used is Acetylcholine acting through an M2 receptor; this is inhibited by Atropine.
• Atropine can therefore be used in extreme bradycardia to speed up the heart.

Sympathetic Supply of the Heart:-

• The Cardiac Sympathetic Nerves supply the SA node, AV node and myocardium.
• They act to increase heart rate and decrease AV nodal delay.
• They also increase the force of cardiac contraction.
• The neurotransmitter used in Noradrenaline.

Cardiac cycle:-

Cardiac cycle:-

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• The cycle diagram depicts one heartbeat of the continuously repeating cardiac cycle, namely: ventricular diastole followed by ventricular systole, etc.
• while coordinating with atrial systole followed by atrial diastole, etc.
• The cycle also correlates to key electrocardiogram tracings: the T wavethe P wave and the QRS 'spikes' complex (ventricular systole)—all shown as color purple-in-black segments.

• The cardiac cycle is the performance of the human heart from the ending of one heartbeat to the beginning of the next.
• It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, dubbed systole.
• After emptying, the heart immediately relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems.
• A normally performing heart must be fully expanded before it can efficiently pump again.
• Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 seconds to complete the cycle.

• There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert to repeat the cardiac cycle continuously,.
• At the start of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria; then, near the end of ventricular diastole–late, the two atria begin to contract, and each atrium pumps blood into the ventricle 'below' it.
• During ventricular systole the ventricles are contracting and vigorously pulsing two separated blood supplies from the heart—one to the lungs and one to all other body organs and systems—while the two atria are relaxed.
• This precise coordination ensures that blood is efficiently collected and circulated throughout the body.

• The mitral and tricuspid valves, also known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling.
• Late in the filling period the atria begin to contract (atrial systole) forcing a final crop of blood into the ventricles under pressure—see cycle diagram.
• Then, prompted by electrical signals from the sinoatrial node, the ventricles start contracting, and as back-pressure against them increases the AV valves are forced to close, which stops the blood volumes in the ventricles from flowing in or out; this is known as the isovolumic contraction stage.

• Due to the contractions of the systole, pressures in the ventricles rise quickly, exceeding the pressures in the trunks of the aorta and the pulmonary arteries and causing the requisite valves to open—which results in separated blood volumes being ejected from the two ventricles.
• This is the ejection stage of the cardiac cycle; it is depicted as the ventricular systole–first phase followed by the ventricular systole–second phase.
• After ventricular pressures fall below their peak(s) and below those in the trunks of the aorta and pulmonary arteries, the aortic and pulmonary valves close again—see, at right margin, Wiggers diagram, blue-line tracing.

• Now follows the isovolumic relaxation, during which pressure within the ventricles begin to fall significantly, and thereafter the atria begin refilling as blood returns to flow into the right atrium and into the left atrium. 
• As the ventricles begin to relax, the mitral and tricuspid valves open again, and the completed cycle returns to ventricular diastole and a new "Start" of the cardiac cycle.
• Throughout the cardiac cycle, blood pressure increases and decreases.
• The movements of cardiac muscle are coordinated by a series of electrical impulses produced by specialized pacemaker cells found within the sinoatrial node and the atrioventricular node.
• Cardiac muscle is composed of myocytes which initiate their internal contractions without applying to external nerves—with the exception of changes in the heart rate due to metabolic demand.
• In an electrocardiogram, electrical systole initiates the atrial systole at the P wave deflection of a steady signal; and it starts contractions.

Electrocardiogram Graph:-

Electrocardiography:-

• Electrocardiography is the process of producing an electrocardiogram. 
• It is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin.
• These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle.
• Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, and electrolyte disturbances.

• In a conventional 12-lead ECG, ten electrodes are placed on the patient's limbs and on the surface of the chest.
• The overall magnitude of the heart's electrical potential is then measured from twelve different angles ("leads") and is recorded over a period of time (usually ten seconds).
• In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle.
• There are three main components to an ECG: the P wave, which represents the depolarization of the atria; the QRS complex, which represents the depolarization of the ventricles; and the T wave, which represents the repolarization of the ventricles.

• During each heartbeat, a healthy heart has an orderly progression of depolarization that starts with pacemaker cells in the sinoatrial node, spreads throughout the atrium, and passes through the atrioventricular node down into the bundle of His and into the Purkinje fibers, spreading down and to the left throughout the ventricles.
• This orderly pattern of depolarization gives rise to the characteristic ECG tracing.
• To the trained clinician, an ECG conveys a large amount of information about the structure of the heart and the function of its electrical conduction system.
• Among other things, an ECG can be used to measure the rate and rhythm of heartbeats, the size and position of the heart chambers, the presence of any damage to the heart's muscle cells or conduction system, the effects of heart drugs, and the function of heart.

Blood pressure:-

• Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels.
• Most of this pressure results from the heart pumping blood through the circulatory system.
• When used without qualification, the term "blood pressure" refers to the pressure in the large arteries.
• Blood pressure is usually expressed in terms of the systolic pressure over diastolic pressure  in the cardiac cycle
• It is measured in millimeters of mercury (mmHg) above the surrounding atmospheric pressure.

• Blood pressure is one of the vital signs—together with respiratory rate, heart rate, oxygen saturation, and body temperature—that healthcare professionals use in evaluating a patient's health.
• Normal resting blood pressure, in an adult is approximately 120 millimeters of mercury (16 kPa) systolic over 80 millimeters of mercury (11 kPa) diastolic, denoted as "120/80 mmHg".
• Globally, the average blood pressure, age standardized, has remained about the same since 1975 to the present, at approx. 127/79 mmHg in men and 122/77 mmHg in women, although these average data mask quite large divergent regional trends.

• Traditionally, blood pressure was measured non-invasively using auscultation with either an aneroid gauge, or a mercury-tube sphygmomanometer.
•  Auscultation is still generally considered to be the gold standard of accuracy for non-invasive blood pressure readings in clinic.
•  However, semi-automated methods have become common, largely due to concerns about potential mercury toxicity, although cost, ease of use and applicability to ambulatory blood pressure or home blood pressure measurements have also influenced this trend.
•  Early automated alternatives to mercury-tube sphygmomanometers were often seriously inaccurate, but modern devices validated to international standards achieve an average difference between two standardized reading methods of 5 mm Hg or less and a standard deviation of less than 8 mm Hg.
•  Most of these semi-automated methods measure blood pressure using oscillometer.

• Blood pressure is influenced by cardiac output, systemic vascular resistance and arterial stiffness and varies depending on situation, emotional state, activity, and relative health.
• In the short term, blood pressure is regulated by baroreceptors which act via the brain to influence the nervous and the endocrine systems.
• Blood pressure that is too low is called hypotension, pressure that is consistently too high is called hypertension, and normal pressure is called normotension.
•  Both hypertension and hypotension have many causes and may be of sudden onset or of long duration.
• Long-term hypertension is a risk factor for many diseases, including heart disease, stroke and kidney failure.
• Long-term hypertension is more common than long-term hypotension.

UNIT-III 

Nerve Physiology:-

1. Nerve Physiology:-

• A nerve is an enclosed, cable-like bundle of nerve called axons, in the peripheral nervous system.
• A nerve transmits electrical impulses and is the basic unit of the peripheral nervous system.
• A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system.
• Each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as some Schwann cells that coat the axons in myelin.

• Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium.
• The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the perineurium.
• Finally, the entire nerve is wrapped in a layer of connective tissue called the epineurium.
• In the central nervous system, the analogous structures are known as nerve tracts.

• Most neurons consist of three parts: the dendrites, which are multiple elongated processes specialized in receiving stimuli from the environment, sensory epithelial cells, or other neurons; the cell body, which is the trophic center for the whole nerve cell and is also receptive to stimuli; and the axon, which is a single process specialized in generating or conducting of nerve impulses to other cells.
• Axons may also receive information from other neurons; this information mainly modifies the transmission of action potentials to other neurons.
• The distal portion of the axon is usually branched and constitutes the terminal arborization.
• Each branch of this arborization terminates on the next cell in dilatations called end bulbs, which interact with other neurons or no nerve cells, forming structures called synapses.
• Synapses transmit the information to the next cell in the circuit.

Neurons

Introduction:- 

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Structures of Neuron:-

• In addition to having all the normal components of a cell (nucleus, organelles, etc.) neurons also contain unique structures for receiving and sending the electrical signals that make neuronal communication possible.

The above image shows the basic structural components of an average neuron, including the dendrite, cell body, nucleus, Node of Ranvier, myelin sheath, Schwann cell, and axon terminal.

Dendrite

• Dendrites are branch-like structures extending away from the cell body, and their job is to receive messages from other neurons and allow those messages to travel to the cell body.
• Although some neurons do not have any dendrites, other types of neurons have multiple dendrites.
• Dendrites can have small protrusions called dendritic spines, which further increase surface area for possible connections with other neurons.

Cell Body

• Like other cells, each neuron has a cell body that contains a nucleus, smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria, and other cellular components.

Axon

• An axon, at its most basic, is a tube-like structure that carries an electrical impulse from the cell body to the structures at opposite end of the neuron—axon terminals, which can then pass the impulse to another neuron.
• The cell body contains a specialized structure, the axon hillock, which serves as a junction between the cell body and the axon.

Synapse

• The synapse is the chemical junction between the axon terminals of one neuron and the dendrites of the next.
• It is a gap where specialized chemical interactions can occur, rather than an actual structure.

Structure of generalised Neuron:-

• A neuron, nerve cell, is an electrically excitable cell^] that communicates with other cells via specialized connections called synapses.
• It is the main component of nervous tissue in all animals except sponges and placozoa. Plants and fungi do not have nerve cells.

• Neurons are typically classified into three types based on their function. Sensory neurons respond to stimuli such as touch, sound, or light that affect the cells of the sensory organs, and they send signals to the spinal cord or brain. 
• Motor neurons receive signals from the brain and spinal cord to control everything from muscle contractions to glandular output. 
• Interneurons connect neurons to other neurons within the same region of the brain or spinal cord.
• A group of connected neurons is called a neural circuit.
• A typical neuron consists of a cell body (soma), dendrites, and a single axon.
• The soma is usually compact.
• The axon and dendrites are filaments that extrude from it.
• Dendrites typically branch profusely and extend a few hundred micrometers from the soma.
• The axon leaves the soma at a swelling called the axon hillock, and travels for as far as 1 meter in humans or more in other species.
• It branches but usually maintains a constant diameter.
• At the farthest tip of the axon's branches are axon terminals, where the neuron can transmit a signal across the synapse to another cell. Neurons may lack dendrites or have no axon.
• The term neurite is used to describe either a dendrite or an axon, particularly when the cell is undifferentiated.

• Most neurons receive signals via the dendrites and soma and send out signals down the axon.
• At the majority of synapses, signals cross from the axon of one neuron to a dendrite of another.
• However, synapses can connect an axon to another axon or a dendrite to another dendrite.
• The signaling process is partly electrical and partly chemical.
• Neurons are electrically excitable, due to maintenance of voltage gradients across their membranes.
• If the voltage changes by a large enough amount over a short interval, the neuron generates an all-or-nothing electrochemical pulse called an action potential.
• This potential travels rapidly along the axon, and activates synaptic connections as it reaches them.
• Synaptic signals may be excitatory or inhibitory, increasing or reducing the net voltage that reaches the soma.
• In most cases, neurons are generated by neural stem cells during brain development and childhood.
•  Neurogenesis largely ceases during adulthood in most areas of the brain.
• However, strong evidence supports generation of substantial numbers of new neurons in the hippocampus and olfactory bulb.

Types of neurons:-

Types of Neurons

• There are three major types of neurons: sensory neurons, motor neurons, and interneurons.
• All three have different functions, but the brain needs all of them to communicate effectively with the rest of the body.

Sensory Neurons

• Sensory neurons are neurons responsible for converting external stimuli from the environment into corresponding internal stimuli.
• They are activated by sensory input, and send projections to other elements of the nervous system, ultimately conveying sensory information to the brain or spinal cord.
• Unlike the motor neurons of the central nervous system (CNS), whose inputs come from other neurons, sensory neurons are activated by physical modalities (such as visible light, sound, heat, physical contact, etc.) or by chemical signals (such as smell and taste).
• Most sensory neurons are psedounipolar, meaning they have an axon that branches into two extensions—one connected to dendrites that receive sensory information and another that transmits this information to the spinal cord.

Motor Neurons

• Motor neurons are neurons located in the central nervous system, and they project their axons outside of the CNS to directly or indirectly control muscles.
• The interface between a motor neuron and muscle fiber is a specialized synapse called the neuromuscular junction.
• The structure of motor neurons is multipolar, meaning each cell contains a single axon and multiple dendrites.
• This is the most common type of neuron.

Interneurons

• Interneurons are neither sensory nor motor; rather, they act as the “middle men” that form connections between the other two types.
• Located in the CNS, they operate locally, meaning their axons connect only with nearby sensory or motor neurons.
• Interneurons can save time and therefore prevent injury by sending messages to the spinal cord and back instead of all the way to the brain.
• Like motor neurons, they are multipolar in structure.

Structure of Synapse:-

• In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell.

• Santiago Ramón y Cajole proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine.
• The word "synapse" – from the Greek synapsis meaning "conjunction", in turn from ("together") and  ("to fasten")) – was introduced in 1897 by the English neurophysiologist Charles Sherrington in Michael Foster's Textbook of Physiology.
•  Sherrington struggled to find a good term that emphasized a union between two separate elements, and the actual term "synapse" was suggested by the English classical scholar Arthur Woollgar Verrall, a friend of Foster.
• Some authors generalize the concept of the synapse to include the communication from a neuron to any other cell type, such as to a motor cell, although such non-neuronal contacts may be referred to as junctions . landmark study by Sanford Paley demonstrated the existence of synapses.

• Synapses are essential to neuronal function: neurons are cells that are specialized to pass signals to individual target cells, and synapses are the means by which they do so.
• At a synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with the membrane of the target cell.
• Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process.
• In many synapses, the presynaptic part is located on an axon and the postsynaptic part is located on a dendrite or soma.
•  Astrocytes also exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission.
• Synapses (at least chemical synapses) are stabilized in position by synaptic adhesion molecules (SAMs) projecting from both the pre- and post-synaptic neuron and sticking together where they overlap; SAMs may also assist in the generation and functioning of synapses.

Major Neurotransmitter:-

Major Neurotransmitter:-

• Neurotransmitters are endogenous chemicals acting as signaling molecules that enable neurotransmission.
• They are a type of chemical messenger which transmits signals across a chemical synapse from one neuron (nerve cell) to another 'target' neuron, to a muscle cell, or to a gland cell.
• Neurotransmitters are released from synaptic vesicles in synapses into the synaptic cleft, where they are received by neurotransmitter receptors on the target cell.
• Many neurotransmitters are synthesized from simple and plentiful precursors such as amino acids, which are readily available and only require a small number of biosynthetic steps for conversion.
• Neurotransmitters are essential to the function of complex neural systems.
• The exact number of unique neurotransmitters in humans is unknown, but more than 200 have been identified.

Mechanism:-

• Neurotransmitters are stored in synaptic vesicles, clustered close to the cell membrane at the axon terminal of the presynaptic neuron.
• Neurotransmitters are released into and diffuse across the synaptic cleft, where they bind to specific receptors on the membrane of the postsynaptic neuron.
• Binding of neurotransmitters may influence the postsynaptic neuron in either an excitation or inhibitory way, depolarizing or repolarizing it respectively.
• Most of the neurotransmitters are about the size of a single amino acid; however, some neurotransmitters may be the size of larger proteins.
• A released neurotransmitter is typically available in the synaptic cleft for a short time before it is metabolized by enzymes, pulled back into the presynaptic neuron through  bound to a postsynaptic receptor.
• Nevertheless, short-term exposure of the receptor to a neurotransmitter is typically sufficient for causing a postsynaptic response by way of synaptic transmission.
• Generally, a neurotransmitter is released at the presynaptic terminal in response to a threshold action potential or graded electrical potential in the presynaptic neuron.
• However, low level 'baseline' release also occurs without electrical stimulation.

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Acetylcholine:-

• Acetylcholine is an organic chemical that functions in the brain and body of many types of animals as a neurotransmitter—a chemical message released by nerve cells to send signals to other cells, such as neurons, muscle cells and gland cells.
•  Its name is derived from its chemical structure: it is an ester of acetic acid and choline.
• Parts in the body that use or are affected by acetylcholine are referred to as cholinergic.
• Substances that interfere with acetylcholine activity are called anticholinergics.

• Acetylcholine is the neurotransmitter used at the neuromuscular junction—in other words, it is the chemical that motor neurons of the nervous system release in order to activate muscles.
• This property means that drugs that affect cholinergic systems can have very dangerous effects ranging from paralysis to convulsions.
• Acetylcholine is also a neurotransmitter in the autonomic nervous system, both as an internal transmitter for the sympathetic nervous system and as the final product released by the parasympathetic nervous system.
•  Acetylcholine is the primary neurotransmitter of the parasympathetic nervous system.

• In the brain, acetylcholine functions as a neurotransmitter and as a neuromodulator.
• The brain contains a number of cholinergic areas, each with distinct functions; such as playing an important role in arousal, attention, memory and motivation.
• Acetylcholine has also been traced in cells of non-neural origins and microbes.
• Recently, enzymes related to its synthesis, degradation and cellular uptake have been traced back to early origins of unicellular eukaryotes.
•  The protist pathogen Acanthamoeba spp.
• Has shown the presence of Ache, which provides growth and proliferative signals via a membrane located M1-muscarinic receptor homolog.
• Partly because of its muscle-activating function, but also because of its functions in the autonomic nervous system and brain, many important drugs exert their effects by altering cholinergic transmission.
• Numerous venoms and toxins produced by plants, animals, and bacteria, as well as chemical nerve agents such as Sarin, cause harm by inactivating or hyperactivating muscles via their influences on the neuromuscular junction.
• Drugs that act on muscarinic acetylcholine receptors, such as atropine, can be poisonous in large quantities, but in smaller doses they are commonly used to treat certain heart conditions and eye problems.
•  Scopolamine, which acts mainly on muscarinic receptors in the brain, can cause delirium and amnesia.
• The addictive qualities of nicotine are derived from its effects on nicotinic acetylcholine receptors in the brain.

Adrenaline:-

Adrenaline:-

• Adrenaline is normally produced by both the adrenal glands and a small number of neurons in the medulla oblongata, where it acts as a neurotransmitter involved in regulating visceral functions (e.g., respiration).
•  It plays an important role in the fight-or-flight response by increasing blood flow to muscles, output of the heart, pupil dilation response and blood sugar level.
• Adrenaline, also known as epinephrine, is a hormone and medication.
•  It does this by binding to alpha and beta receptors.
•  It is found in many animals and some single-celled organisms.
• Polish physiologist Napoleon Cybulski first isolated adrenaline in 1895.

Medical uses:-

• As a medication, it is used to treat a number of conditions including anaphylaxis, cardiac arrest, and superficial bleeding.
•  Inhaled adrenaline may be used to improve the symptoms of croup.
•  It may also be used for asthma when other treatments are not effective.
• It is given intravenously, by injection into a muscle, by inhalation, or by injection just under the skin.
•  Common side effects include shakiness, anxiety, and sweating.
• A fast heart rate and high blood pressure may occur.

• While the safety of its use during pregnancy and breastfeeding is unclear, the benefits to the mother must be taken into account.
• A case has been made for the use of adrenaline infusion in place of the widely accepted treatment of inotropes for preterm infants with clinical cardiovascular compromise.
• Occasionally it may result in an abnormal heart rhythm.
• Although there is sufficient data which strongly recommends Adrenaline infusions as a viable treatment, more trials are needed in order to conclusively determine that these infusions will successfully reduce morbidity and mortality rates among preterm, cardiovascular compromised infants.

Dopamine:-

Dopamine:-

• Dopamineis a hormone and a neurotransmitter that plays several important roles in the brain and body.
• It is an organic chemical of the catecholamine and phenethylamine families.
• It is an amine synthesized by removing a carboxyl group from a molecule of its precursor chemical L-DOPA, which is synthesized in the brain and kidneys.
• Dopamine is also synthesized in plants and most animals.
• In the brain, dopamine functions as a neurotransmitter—a chemical released by neurons (nerve cells) to send signals to other nerve cells.
• The brain includes several distinct dopamine pathways, one of which plays a major role in the motivational component of reward-motivated behavior.
• The anticipation of most types of rewards increases the level of dopamine in the brain, and many addictive drugs increase dopamine release or block its reuptake into neurons following release.
• Other brain dopamine pathways are involved in motor control and in controlling the release of various hormones.
• These pathways and cell groups form a dopamine system which is neuromodulatory.

• In popular culture and media, dopamine is usually seen as the main chemical of pleasure, but the current opinion in pharmacology is that dopamine instead confers motivational salience ; in other words, dopamine signals the perceived motivational prominence of an outcome, which in turn propels the organism's behavior toward or away from achieving that outcome.
• Outside the central nervous system, dopamine functions primarily as a local paracrine messenger.
• In blood vessels, it inhibits norepinephrine release and acts as a vasodilator; in the kidneys, it increases sodium excretion and urine output; in the pancreas, it reduces insulin production; in the digestive system, it reduces gastrointestinal motility and protects intestinal mucosa; and in the immune system, it reduces the activity of lymphocytes.
• With the exception of the blood vessels, dopamine in each of these peripheral systems is synthesized locally and exerts its effects near the cells that release it.

• Several important diseases of the nervous system are associated with dysfunctions of the dopamine system, and some of the key medications used to treat them work by altering the effects of dopamine.
•  Parkinson's disease, a degenerative condition causing tremor and motor impairment, is caused by a loss of dopamine-secreting neurons in an area of the midbrain called the substantiating.
• Its metabolic precursor L-DOPA can be manufactured; Levodopa, a pure form of L-DOPA, is the most widely used treatment for Parkinson’s.
• There is evidence that schizophrenia involves altered levels of dopamine activity, and most antipsychotic drugs used to treat this are dopamine antagonists which reduce dopamine activity.
•  Similar dopamine antagonist drugs are also some of the most effective anti-nausea agents.
•  Restless legs syndrome and attention deficit hyperactivity disorder (ADHD) are associated with decreased dopamine activity.
• Dopaminergic stimulants can be addictive in high doses, but some are used at lower doses to treat ADHD. 
• Dopamine itself is available as a manufactured medication for intravenous injection: although it cannot reach the brain from the bloodstream, its peripheral effects make it useful in the treatment of heart failure or shock, especially in newborn babies.

Conduction of nerve impulse:-

• A nerve impulse is the electric signals that pass along the dendrites to generate a nerve impulse or an action potential.
• An action potential is due to the movement of ions in and out of the cell.
• It specifically involves sodium and potassium ions.
• They are moved in and out of the cell through sodium and potassium channels and sodium-potassium pump.
• Conduction of nerve impulse occurs due to the presence of active and electronic potentials along the conductors.
• Transmission of signals internally between the cells is achieved through a synapse.
• Nerve conductors comprise relatively higher membrane resistance and low axial resistance.
• The electrical synapse has its application in escape reflexes, heart and in the retina of vertebrates.
• They are mainly used whenever there is a requirement of fast response and timing being crucial.
• The ionic currents pass through the two cell membrane when the action potential reaches the stage of such synapse.

Mechanism of Transmission of Nerve Impulse:-

• The axon or nerve fibers are in the form of a cylinder wherein the interior of the axon is filled with axoplasm and the exterior is covered with axolemma.
• The nerve fibers are immersed in ECF.
• The solution is in the ionic form that is present in axoplasm and extracellular fluid or ECF.
• Outside the axon, the negatively charged chloride ions are neutralized in the presence of positively charged sodium ions.
• Negatively charged protein molecules are neutralized in the presence of potassium ions within the axoplasm.
•  The membrane of a neuron is –ve inside and +ve outside.
• Resting potential would be the difference in charge.
• The difference in charge might vary from seventy to ninety millivolts, as a result, the membrane would be polarized.
• Sodium potassium pump operates to keep resting potential in equilibrium.
• The pump is placed on the axon membrane.
• Now the potassium ions are pumped from ECF to axoplasm and sodium ions are pumped from axoplasm to ECF.
• The sodium-potassium pump stops operating when a stimulus is applied to a membrane of a nerve fiber.
• The stimulus could be either electrical, chemical or mechanical.

• The potassium ions rush outside the membrane and sodium ions rush inside the membrane as a result negative charges are present outside and positive charges are present inside.
• The nerve fibers are either depolarized or they are said to be in the action potential.
• The action potential travelling along the membrane is called the nerve impulse.
• It is around + 30 mV.
• The sodium-potassium pump starts to operate once the action potential is completed.
• As a result, the axon membrane will obtain a resting potential by repolarization.
• Now the process takes place in reverse order.
• It is a reversal of the process that has taken place during an action potential.
• Here, potassium ions will be rushed inside and sodium ions will be rushed outside.
• Impulse would not be transmitted through the nerve fiber during the refractory period.
• In the case of white fibers, saltatory propagation takes place.
• That is impulse jumps from node to node and it increases with increase in the speed of nerve impulse.
• It is around twenty times faster compared to that of the non-medullated nerve fibers.
• The transmission of nerve impulse would rely upon the diameter of the fiber.
• For instance, the nerve impulse of a mammal is one twenty meters per second whereas nerve impulse of a Frog is 30 meters per second.

2.Muscles Physiology:-

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Introduction:-

• There are three major muscle types found in the human body: skeletal, cardiac, and smooth muscle.
• Each muscle type has unique cellular components, physiology, specific functions, and pathology.
• Skeletal muscle is an organ that primarily controls movement and posture.
• Cardiac muscle encompasses the heart, which keeps the human body alive.
• Smooth muscle is present throughout the gastrointestinal, reproductive, urinary, vascular, and respiratory systems.

Cellular:-

• Skeletal muscle constitutes approximately 40% of the total human body weight.
• Its composition is many individual fibers that are bundled together into a muscle spindle; this is what gives the skeletal muscle a striated appearance.
• A single muscle fiber is composed mostly of actin and myosin fibers that are covered by a cell membrane.
• These fibers are the functional unit of the organ, leading to contraction and relaxation.
• There are two major classifications of skeletal muscle; these include Type I and Type II.
• The vast diversity in the makeup of skeletal muscle leads to variations in speed and length of contractions in different muscle groups, depending on their specific function.

• Cardiac muscle or myocardium is an involuntary, striated muscle that encloses the chambers of the heart.
• It is comprised of individual cardiomyocytes, which are similar in structure to skeletal muscle.
• Each cardiomyocyte contains cytoskeletal and contractile elements, all of which are connected through intercalated discs.
• These are highly adherent complexes, which allow the cardiac muscle cells to receive rapid electrical transmission and contract as a single unit.
•  Cardiac muscle also contains specialized cardiac pacemaker cells that lie within the myocardium.
• These cells allow for cardiac tissue to depolarize without external stimuli intrinsically.
• The cells of smooth muscle are also composed of actin and myosin fibers; however, they are arranged in sheets rather than spindles which give this type of muscle a smooth appearance.
• These cells are present in the walls of many organs such as the lungs, gastrointestinal tract, reproductive organs, blood vessels, and even in the skin.

Function:-

• The muscle in the human body, whether it is skeletal, cardiac, or smooth, functions to create force and movement.
• Muscles of the skeleton support the bones to maintain posture as well as control voluntary movement.
• Skeletal muscle also contributes to energy metabolism and storage.
• Cardiac muscle propels blood and leads to proper oxygenation and maintenance of each cell that comprises the human body.
• Smooth muscle is located throughout the body and uses contractile force for shortening and propelling various contents across the lumen of the multiple organ systems in which it is involved.

Mechanism:-

• Action potentials from nerve fibers of the central nervous system depolarize muscle down the length of the sarcolemma to the innermost fibers through a transverse tubule system.
• The action potential responds with a dihydropyridine receptor on the T tubule; this acts as a voltage sensor allowing for calcium to be released.
• Calcium subsequently activates ryanodine receptors in the sarcoplasmic reticulum to release even more calcium.
• Higher quantities of calcium can then bind to the protein troponin that is located on the actin filaments.
• The calcium-troponin complex displaces the protein tropomyosin from the active site of the actin filament and allows for myosin binding and muscle contraction.
• Adenosine triphosphate (ATP) is needed to detach myosin from the actin filaments and allow for muscle relaxation.

• In a similar fashion to skeletal muscle, cardiac muscle is triggered by calcium binding to troponin in the actin filaments of the cardiomyocyte.
• This binding then removes tropomyosin and allows for the binding of myosin to actin filaments and eventual contraction.
• The significant difference between cardiac and skeletal muscle is in the cardiomyocyte's automaticity.
• Specialized cardiac pacemaker cells located in the sinoatrial (SA) node are responsible for creating cardiac muscle contraction.
• These act to trigger action potentials that allow for sodium and potassium influx as well as calcium release from the sarcoplasmic reticulum.
• The cardiac muscle can then contract as a single, coordinated unit.

• Smooth muscle contraction is not under voluntary control and is done so through the autonomic regulation of a calcium-calmodulin interaction.
• Contraction begins through a change in action potential or activation of mechanical stretch receptors in the plasma membrane.
• Intracellular calcium is increased and combines with the protein calmodulin.
• It is this complex that activates the myosin light chain (MLC) kinase to phosphorylate and form cross-bridges between myosin and actin, leading to muscle contraction.
• Some smooth muscle maintains tone, which is caused by a constant phosphorylation level in the absence of external potentials.
• A decrease in intracellular calcium levels induces relaxation.

Clinical Significance:-