Organ Systems

Gas Exchange

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Gas Exchange

Introduction

Gas Exchange

Gas Exchange

Introduction

The whistle blows and practice is over, so you run in from the field. You’re out of breath from all the running you’ve been doing for the past hour. But have you ever wondered what causes you to become out of breath or even why breathing faster seems to help you recover?

Photo: https://www.flickr.com/photos/80778878@N00/1325427729

When you run, your body uses energy that is taken from the food you eat every day. Cells can only obtain the energy from your food if there is a special gas called oxygen in your body (see our Cells Are Us Module for more on how the body uses oxygen). Oxygen in the air is brought into your lungs when you inhale. Blood picks up the oxygen from your lungs and carries it through the bloodstream to every cell in your body.

Cells use the oxygen and produce another gas, called carbon dioxide, as a waste product. It is very dangerous if carbon dioxide builds up in your body, so your blood carries the carbon dioxide to your lungs where it is released into the air when you breathe out or exhale.

This unit will help you understand how the gas exchange between oxygen and carbon dioxide occurs in the body and why it is so important.

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• After completing this lesson, each student should be able to:

Objectives

Gas Exchange

• Understand the structure and function of the respiratory and circulatory systems.
• Explain how the processes of gas exchange occur and what purpose they serve.
• Explain the harmful effects that smoking and air pollution have on the body.

Why It Matters

Gas Exchange

The Delicate Balance of Gas Exchange

Gas Exchange

Why It Matters

You know that you breathe in oxygen and breathe out carbon dioxide. Each cell in your body requires oxygen in order to obtain energy. Without the energy for these life functions, your individual cells would die. Carbon dioxide gas is a waste product of cells and is toxic if allowed to build up in your cells. If there is a severe lack of oxygen or too much carbon dioxide builds up, too many cells would die. That would cause the entire organism to die.

Picture from: https://doctorlib.info/physiology/textbook-medical-physiology/42.html

Cross cuts of lung tissue. The purple lines are lines of cells. The open spaces are the air sacs that need to be open in order to breathe. Normal lung is on the left. The air sacs are open and the lines of cells lining the sacs are thin. Pneumonia (middle picture) is usually caused by infections of the lung that cause the cells lining air sacs to swell ("edema") and the air spaces to fill with blood cells, fluid, and cellular debris. Emphysema (right-hand picture) is usually caused by smoking, which breaks down the air sacs, making them lose their elastic properties and keeping them from emptying air properly.

The Delicate Balance of Gas Exchange Cont’d

Gas Exchange

Why It Matters

These critical gases (oxygen and carbon dioxide) have to be transported through the entire body. The oxygen needs to go to the cells that need it, and the carbon dioxide needs to be removed from the cells, so it doesn’t build up. Blood carries these gases. Blood vessels are needed to provide a pathway for the blood, and the heart is needed to pump the blood and its gases through the vessels. Blood needs to circulate to the cells where it drops off oxygen and picks up the carbon dioxide waste. From there it makes its way to through the body to the lungs where it can come in contact with outside air. The lungs are the place where gas exchange with air takes place (in fish, gills serve the same purpose). Oxygen-deficient blood coming from cells picks up oxygen from the air in the lungs. At the same time, the surplus carbon dioxide is given off to outside air.

Picture from: https://doctorlib.info/physiology/textbook-medical-physiology/42.html

Some 50 years ago, there was a worldwide epidemic of polio, which caused paralysis. Most victims were children. Some unfortunate children had paralysis of the muscles used in breathing. In order to breathe, they had to spend their life in "iron lungs" such as the one diagrammed above.

What We Know

Gas Exchange

Gas Exchange

What We Know

Blood Gases

Gas exchange occurs through blood. Blood circulates through the body, exchanging gases with tissues, and circulates in the lungs, exchanging gases with the air. This process involves two body systems: the respiratory system and the circulatory system.

Only two gases are important in this discussion, oxygen and carbon dioxide. Our unit on energy in the Cells Are Us module goes into more detail on why these are the two we are focusing on. It is because they are the gases most important to converting the food we eat into energy for our bodies. The body uses oxygen for converting food into energy, and the body produces carbon dioxide as a waste product of that process.

Why are we not focusing on nitrogen in this lesson, which makes up 78% of the air? Nitrogen does not normally exchange in the sense that we discuss oxygen and carbon dioxide. Nitrogen only becomes important in scuba diving, where it bubbles out of the tissues if you have been deep in the water.

Gas Exchange

What We Know

How Gas Amount Changes

Oxygen is consumed by cells in the process of converting food into energy. It thus has to be replenished, and air is the only source.

Carbon dioxide is a waste product of the Krebs cycle, which is the sequence of reactions by which most living cells generate energy. Carbon dioxide needs to be continually removed from the tissues that generate it. If left to accumulate, carbon dioxide forms an acid (carbonic acid), which would alter the normal function of body enzymes. For these exchanges to occur, blood must circulate between lungs (in the respiratory system) and tissue, a function which is carried out by the heart and blood vessels (the circulatory system).

Gas Exchange

What We Know

What We Know About Gas Exchange in the Lungs

Oxygen & Carbon Dioxide

The body requires oxygen in order to produce energy for our cells to do work. Therefore, it is essential that we have an efficient system of obtaining oxygen from the air. Our bodies also produce a toxic gas called carbon dioxide that must be efficiently removed from the body to prevent cell damage. When we inhale, we pick up oxygen from air. When we exhale, we flush out carbon dioxide.

Each breath lasts only a few seconds (even less if we are running.) Isn't it amazing that gas exchange occurs so quickly? What is it about gases that lets them exchange so quickly?

The Respiratory System

The primary function of the respiratory system is gas exchange. It accomplishes this by:

• Bringing in oxygen rich air into the body and into the proximity of the circulatory system.
• Taking up carbon dioxide brought to the lungs via the blood and expelling it out of the body.

So the respiratory system brings oxygen to the blood and exchanges it with carbon dioxide that needs to be removed from the blood.

Gas Exchange

What We Know

What We Know About Gas Exchange in the Lungs Cont’d

The Structures of the Respiratory System

Here is a list of structures to become familiar with:

• Mouth and Nose- these are the openings where respiratory gases enter and leave the body.
• Pharynx and Larynx- these are the structures that connect the nose and mouth to the trachea. The pharynx connects to both the respiratory and digestive systems. The larynx contains the vocal cords which produce sound when air causes them to vibrate.
• Trachea (windpipe)- this passage way connects the larynx to the lungs.
• Bronchial tube- the trachea breaks up into these smaller tubes to enter the right and left lungs.
• Lungs- these are the balloon-like structures that temporarily hold air in the body.
• Bronchioles- within the lungs the bronchi split into these even smaller tubes which attach to the alveoli.
• Alveoli- these are the small sac-like structures where gas exchange occurs with the blood. Singular is “alveolus.”

Note: The above structures are listed in the order they are used during inspiration (inhaling) and in reverse order for expiration (exhaling).

Gas Exchange

What We Know

What We Know About Gas Exchange in the Lungs Cont’d

Here is a detailed picture of the respiratory system. The structures we will discuss are highlighted. 

Do you see how air moves into the lungs?

Why do you think the bronchi become so branched?

Why do you think there are veins and arteries at the alveoli?

What keeps food from going into the lungs?

Gas Exchange

What We Know

What We Know About Gas Exchange in the Lungs Cont’d

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Here are a few things that will help answer some of your questions:

Source: NIH National Cancer Institute

• Air enters your body through your mouth and nose. The nasal passage connects to the oral passage at the back of the mouth where a tube called the trachea connects the mouth and nose to the lungs. Dirt from the air is filtered before it ever reaches the lungs by the hairs and mucus in the nose. This hair and mucus trap some of the dirt and germs found in the air to protect the lungs from infection. Why do you think we have nose hairs?
• The pharynx, that includes the larynx (that contains the vocal cords that make sound so you can talk), is the passage that the air passes through on the way from the nose or mouth to the trachea. The trachea, or windpipe, is a tube that connects the nose and mouth to the lungs. You can see and feel your trachea on the front of your neck. The tube has C-shaped cartilaginous rings wrapped around it to prevent the tube from collapsing and blocking the air flow to and from the lungs. Air is the only substance designed to go down the trachea. 

Why do you think the trachea is only meant for air? What happens if something blocks the trachea?

Gas Exchange

What We Know

What We Know About Gas Exchange in the Lungs Cont’d

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Image from: NIH

• A little flap in the larynx called the epiglottis covers the trachea each time you swallow to direct food and drinks to go down the esophagus, a tube that leads to the stomach. When food and drinks find their way into the trachea, you’ll know it immediately! You’ll begin coughing in order to push the food back out of the trachea to allow air to pass through uninhibited.

What happens when a person laughs so hard that milk can come out of their nose?

• As the trachea approaches the lungs, it branches into two tubes. One tube leads to the right lung, and the other tube leads to the left lung. These tubes are known as the bronchial tubes. The bronchial tubes enter the lungs and begin branching into smaller and smaller tubes. 
• These smaller tubes are called bronchioles. The walls of the bronchioles contain smooth muscle that is used to dilate or constrict the lungs depending upon the body’s need for oxygen. The bronchioles continue the branching process until they reach small, thin sacs called alveoli. The function of the lungs depends primarily on these tiny structures.

Does this branching allow the tubes to fill the lungs more effectively?

Gas Exchange

What We Know

What We Know About Gas Exchange in the Lungs Cont’d

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Asthma is a disease in which dust, pollen, or other things to which you are allergic change the diameter of the bronchioles. What does this do? Why?

What is the benefit of having such a large amount of surface for gas exchange to take place?

How about a look at a pair of lungs?

These are sheep lungs with a cut trachea at the top. Left: lateral (side) view as seen from animal's right side. Right: back side of the lung, with heart removed. Look closely at the end of the trachea (highlighted) in the picture on the right to see how it branches into the bronchi.

Next, we're going to discuss the alveoli in detail.

Gas Exchange

What We Know

Gas exchange in the lungs

Alveoli

Alveoli are tiny balloon-like sacs in the lungs where gas exchange takes place, and they serve as the barrier between the external environment (the air) and the internal environment (the blood).

Now, the respiratory system meets up with the circulatory system. Because gas must exchange in a second or two between blood vessels (circulatory system) and the air inside of our lungs (the respiratory system), how do you suppose the process is made efficient?

• These small alveoli have very thin walls that are full of blood vessels called capillaries. The walls are so thin that the oxygen, brought in during inhalation, can diffuse through them to enter your blood. 
• Likewise, carbon dioxide is carried by your blood to the blood vessels in the alveoli where it diffuses through the thin walls and into the air in your lungs. That "used" air is now ready for exhalation. Each lung has millions of alveoli, and your body needs all of them to get enough oxygen into your blood! 

Gas Exchange

What We Know

Gas exchange in the lungs Cont’d

This microscopic image shows the thin-walled alveoli as open areas for gases, and the very thin capillaries with red blood cells lined up in them to receive oxygen and drop off carbon dioxide.

Why are there so many capillaries at the alveoli? In the diagram on the previous slide, why are they shown in blue and red?

What is the problem with the buildup of tar and other hazardous materials from smoking in the alveoli of the lungs?

Why is wearing dust masks during work so important for some jobs?

Gas Exchange

What We Know

Why are Veins Labeled in Blue?

Do we really have blue blood? No! The blood in veins is not really blue, even though it is labeled that way. The blood labeled as blue is more of a dark red color, close to maroon. This is different than the bright red blood in the arteries. This change in color is due to the lack of oxygenation in the hemoglobin (oxygen carrying molecule) of the blood. However, during surgery and dissections, the veins that carry this blood can appear blue due to reflection and refraction of light.

• Deoxygenated (labeled blue) blood travels into the capillaries surrounding the alveoli. The blood drops off its carbon dioxide molecules and picks up oxygen. Once the blood cells pick up oxygen, it becomes oxygenated (labeled red) blood. The blood now exits the pulmonary capillaries and carries oxygen to all the tissues in the body.
• Deoxygenated blood does contain oxygen, but it is present at a smaller concentration than oxygenated blood. The term deoxygenated is used for convenience.

Does anybody really have blue blood? Why do bruises appear blue at first (they change to a yellowish color later as the blood is chemically broken down)?

Gas Exchange

What We Know

Muscles involved in Gas Exchange

The muscular system also comes into play during the process of gas exchange.

Image Source: Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013.

• Breathing requires the help of a muscle known as the diaphragm. 
• The diaphragm is a large, sheet-like muscle at the bottom of your chest cavity. It helps you exhale and inhale by moving up and down, respectively. 
• When your diaphragm contracts (moves down), you inhale air. 
• When your diaphragm relaxes (moves up), you exhale air. 
• Without your diaphragm, your lungs couldn’t fill up with fresh air or push old air out.

Why do you think the diaphragm is located at the bottom of your chest cavity?

Gas Exchange

What We Know

The System for Transporting Gases

Your heart beats with about the strength it takes to squeeze a tennis ball. Squeeze a tennis ball and see how hard that is. Now think what it must be like for your heart to do this 70 times a minute, 60 minutes an hour, 24 hours a day - for a lifetime!

The Circulatory System

The heart, the blood, and the blood vessels make up a system for the transport of gases, nutrients, and chemical wastes. The primary functions of the circulatory system are the following:

• To transport nutrients and oxygen to the cells.
• To remove waste and carbon dioxide from the cells.
• To provide for efficient gas exchange.

Blood vessels allow oxygenated blood and nutrients to reach the tissues and wastes to be removed from the tissues.

The blood is the medium (substance and pathway) that carries oxygen and nutrients to the tissue and is also the medium by which waste is transported to the appropriate locations.

Gas Exchange

What We Know

The Heart

The heart is made up of cardiac muscle and is divided into four different chambers. The top two compartments are called atria, while the bottom two compartments are called ventricles.

Cow heart with part of the wall cut away to show interior of a pump chamber (ventricle). Note the valve at the top of the chamber. When blood fills the artery (part of its wall is also cut away) during contraction of the ventricle, the backpressure closes the valve.

Interior anatomy of the human heart

Exterior view of the human heart

Gas Exchange

What We Know

Blood Vessels

There are three basic types of blood vessels:

• Arteries- these carry "oxygen rich" blood away from the heart, except in the case of the artery to the lungs.
• Capillaries- these are the sites of gas exchange between the tissues.
• Veins- these return "oxygen poor" blood to the heart, except for the vein that carries blood from the lungs.

On the right is a diagram showing how the three connect. Notice the artery and vein are much larger than the capillaries. This junction is called a capillary bed.

• The capillaries have very thin walls, and there are many of them.

Why do you think this is?

Why are the capillaries shown with two different colors?

Why is the vein shown as blue?

Click here to watch an animation of the heart beating

Gas Exchange

What We Know

Blood Vessels Cont’d

The circulatory path of blood

Note: Arterial blood (oxygen rich blood) is in red, and venous blood (contains less oxygen) is in blue.

Now, can you draw the parts of the circulatory system and show which parts contain oxygen-rich blood and which parts contain oxygen poor blood?

Let’s take a look at Blood Pressure and how it relates to the system for transporting gases.

Gas Exchange

What We Know

Blood Flow

For gas exchange to occur in the lungs and the rest of the body's tissues, blood must flow continuously through the tissues. The heart pushes blood through the tissues and provides a constant force for blood flow to occur.

The heart provides enough force to propel the blood through the arteries and veins in the body. The arteries entering tissues, called arterioles, can constrict (become more narrow) or dilate (become relaxed and less narrow) to change the amount of blood flowing to an area. If an arteriole constricts, less blood is available for the tissues it supplies. If an arteriole dilates, more blood reaches the tissues it supplies.

Why is it useful for the arteries to change size?

Can you think of situations where certain tissues may need more or less blood flow?

The blood vessel on the right allows four times as much blood flow as the vessel on the left. You can calculate this by using the formula for the area of a circle, which is Area = pi x radius².

Gas Exchange

What We Know

Blood Flow Cont’d

Blood Pressure

Blood pressure is the pressure (force over a given area) exerted by blood on the walls of blood vessels.

• This pressure depends on the amount of blood in the body, the diameter of the blood vessels, and how hard the heart is pumping blood. 
• Resistance in the circulatory system is caused by the blood rubbing against the walls of the blood vessels as it flows through them. This rubbing produces resistance, a force that acts opposite to the blood flow.
• A large vessel is less resistant than a small blood vessel because relatively less blood rubs against the walls of the blood vessel, while a small blood vessel is more resistant because it has a smaller area for the blood to flow through. This means that more blood rubs against the walls of the vessel, and it slows blood flow.
• In any one capillary, this resistance is an advantage because the slowed blood flow allows more time for gas exchange to occur.

Gas Exchange

What We Know

Blood Flow Cont’d

Blood Pressure

• When an arteriole dilates, the diameter almost doubles. When a vessel's diameter increases, the blood flow increases by four times the original amount. 
• This is like the difference between a water hose with a 1/2" inner diameter and a 1" inner diameter water hose. Under the same pressure, the 1" hose will have four times the flow of the smaller hose. 
• With decreased resistance, more blood can flow to the tissues that need more nutrients and gas exchange. For example, under conditions of moderate exercise, blood flow to skeletal muscles can increase by up to 10 times because the arterioles in that area become dilated and supply more blood to the muscles. 
• Under conditions of little resistance, the heart does not have to work as hard to move blood into the tissues.

Gas Exchange

What We Know

Blood Flow Cont’d

Blood Pressure

Is it better for the heart to work less to move blood through the tissues? Why?

What happens to blood flow if the heart is not working hard enough?

A normal cardiac artery with little buildup of fats and cholesterol.

A cardiac artery with severe buildup of cholesterol that is reducing the diameter of the vessel.

Gas Exchange

What We Know

Blood Flow Cont’d

When the blood pressure in the body is elevated, the heart must work very hard to provide adequate blood flow to the tissues. 

• Many people have blood pressure that is too high (called hypertension). One known cause of hypertension is atherosclerosis. Atherosclerosis is a condition in which the walls of the blood vessels become thick and stiff, reducing their flexibility and ability to dilate. 
• Eventually fats and cholesterol build up and reduce the diameter of the blood vessels, making it very difficult for blood to flow through the vessel. In some cases, blood is unable to flow at all. This puts a tremendous amount of stress on the heart and can lead to heart failure. 
• When an artery supplying the brain or heart is blocked, tissue damage can occur very quickly and, if not treated immediately, is permanent and can lead to death.

The nicotine in cigarettes and chewing tobacco increases blood pressure because it causes the arterioles to constrict, while increasing heart rate. Both stress the heart. See Hazards.

How We Know

Gas Exchange

Gas Exchange

How We Know

Today a large number of scientists are working very hard to learn more about the body systems that affect gas transport and the diseases that affect it. Let's take a closer look at how they discovered the things we know about the respiratory system.

How do we measure breathing?

Gas Exchange

How We Know

A spirometer is a piece of equipment that scientists use to measure lung capacity and the amount of air a person normally breathes in and out. You will have an opportunity to make your own spirometer in activity #1.

 A modern electronic spirometer

Image: By National Heart Lung and Blood Institute (NIH)

How do we measure breathing? Cont’d

Gas Exchange

How We Know

Basic idea of measuring air exchange, using a "spirometer." As air is taken in (from the "oxygen chamber" in the apparatus on the left), the floating drum drops down. At the same time the writing arm on the recording drum moves up, indicating inhalation. Opposite effects occur during exhalation.

How can you make a good estimate of the amount of air you breathe in a day?

• One way to do this is to multiply the amount of air you breathe in one breath x the number of breaths you take in a minute x 1440, which is the number of minutes in a day.
• Can you think of any other ways?

How do we measure breathing? Cont’d

Gas Exchange

How We Know

Every day our body breathes in and out as much as 10,000 liters of air. If we were talking about soda, this would be enough soda to fill 5000 two-liter bottles. 5000 bottles of soda weigh about the same as 11 average size cars. Knowing that a bottle of soda ways about 4.4 pounds and an average size car ways 2000 pounds, can you figure out how to make this calculation?

5000 Bottles Soda x 4.4 pounds = 22,000 pounds

and 11 Cars x 2000 pounds = 22,000 pounds

You can make a good estimate of how much air you breathe in and out every day. To do this, observe your breathing rate by counting the number of breaths you take in a minute, and use a spirometer to figure out how much air you breathe in during a single breath at rest (about 0.300 liters is average for a 12- to 13-year-old).

A spirometer can tell a doctor how far a respiratory disease has progressed and help determine what the treatment should be. One of the more common breathing problems in children is asthma, an allergy disease that causes chronic inflammation and swelling of the bronchial tubes. This limits the amount of air that a person can breathe in and out at a given time.

How do we know how lungs work?

Gas Exchange

How We Know

Sometimes the best way to find out how something works is to take it apart and figure out what the smaller parts do. That's exactly what scientists have done to learn about the lungs. Some people donate their bodies to medical schools after they die so that doctors can study the parts and try to figure out how they work. Animal studies have also been used to learn about the lungs. Scientists look closely at all of the different parts of the lung, including the alveoli, bronchiole, bronchial tubes, membrane linings, and the different lobes of the lung.

A healthy lung

How do we know how lungs work? Cont’d

Gas Exchange

How We Know

In living people, physicians can view the inside of the lung using a fiber optic camera, called an endoscope. Using an endoscope, physicians can observe the lung while it is moving and observe very closely the changes that take place during respiration.

Scientists have also learned about the gas exchange that takes place in the lungs by sampling the air directly. They have learned what makes up inspired air and how it differs from air deep within the lungs. For example, they have learned that when air enters the lung it is greatly humidified in order to facilitate gas exchange. In order to do this, the lung makes the air a bit "thicker" and causes it to stay in the lungs longer, increasing contact time and gas exchange. This is the reason that it is sometimes easier to breathe in a room with a humidifier.

Inside of a trachea as seen in an endoscopy procedure

How do we know what happens to the air we breathe?

Gas Exchange

How We Know

In most diagrams, arteries are shown in red, and veins are shown in blue. In reality, veins are a very dark red or have a purple shade.

A simple way of following air through our body is to look at the color of blood. When blood is bright red it means that oxygen is bound to the hemoglobin in the blood. When less oxygen is in the blood, the blood becomes a darker shade of red, very close in color to maroon. 

• Most arteries carry oxygenated blood from the heart to the rest of the body. As the oxygen is released into the tissues, the blood slowly turns a darker shade of red and returns to the heart in veins. 

• Most arteries will look pink to reddish in color, while veins appear darker red or bluish-purple color. When you look at veins through your skin, they can appear blue, depending on your skin color. This is because of the reflection and refraction of light through your skin. This is also the reason the veins are labeled as blue in diagrams.
• Arteries are thick and muscular. Veins are thin and flaccid (loose). 
• From dissection of an animal body, you can see where oxygen is going from the heart by following the arteries. You can see where carbon dioxide is leaving by following the veins back to the heart (See Story Time about how the circulation paths were discovered).

How do we know what happens to the air we breathe? Cont’d

Gas Exchange

How We Know

What you can NOT see (without a microscope) is how arteries are connected to veins.

• The heart has an artery that carries blood to the lungs to pick up oxygen, and release carbon dioxide; this is the only artery in the body that does not have oxygen-rich blood.
• When blood from the heart reaches the lungs, the carbon dioxide leaves the blood much like the carbon dioxide that leaves a coke bottle when it is opened.

Carbon dioxide moves from high to low areas of concentration like the carbon dioxide bubbles in this soda. The same is true for oxygen. 

A device that doctors use to measure oxygen in the blood is an oximeter. An oximeter is clipped on a finger or ear lobe and uses light beams to determine how much oxygen is attached to the hemoglobin in the blood cells. This reflects the amount of oxygen getting into the blood stream. Some oximeters also provide sensors for carbon dioxide levels to help make sure its levels are not toxic. A more accurate measure of testing the body's oxygen levels is to test the blood directly by taking a small blood sample from an artery.

A pulse oximeter

How do we know about gas exchange in body tissues?

Gas Exchange

How We Know

Scientists measure oxygen and carbon dioxide in various heart chambers and blood vessels. They notice that the big changes in both oxygen and carbon dioxide occur in the small capillaries because the gas composition is very different between blood entering a capillary bed and blood leaving it. How do the gases get from the blood to the cells in the body?

• As the blood gets closer to its destination, blood vessels get smaller and thinner until they get so small and thin that gases and other molecules can freely move in and out of the blood stream. 

Why do gases move in and out of the blood? 

• The idea is similar to diffusion, which you can read more about in our Cells Are Us Module. What this means is that if there is more oxygen in the blood, some will move into the cells that need oxygen. 
• The cell is always using up oxygen and needs more from the blood. We know this because we can observe the color change from red to maroon of blood as oxygen is released from the blood to the tissues.

How do we know about gas exchange in body tissues? Cont’d

Gas Exchange

How We Know

As the cell uses oxygen, it produces carbon dioxide. The carbon dioxide diffuses from the cell into the blood. How do we know this? Scientists have come up with clever ways of measuring the concentrations of gases at these locations.

• For example, to measure the concentration of carbon dioxide, scientists measure the acidity of the blood (carbon dioxide in blood converts to an acid compound). 
• To measure acidity, scientists measure the acidity of the solution with a pH meter.
• The higher the concentration of carbon dioxide, the more acidic the blood is and the more toxic it is for the cells. 
• The enzymes that make cells work function best when the cells are not acidic. The further a cell gets from its "optimal" acidity level, the less effective its enzymes become and the more likely the cell is to die.

Meter for measuring acidity

You can observe this effect of acid build-up after you exercise very hard. You may feel a bit of a "burn" in your muscles. This "burn" is acid buildup in the muscles due to a buildup of carbon-dioxide in the cells.

William Harvey (1578-1657)

Storytime

Gas Exchange

Valentine's Day is only five days away as this story is being written. On Valentine's Day we think of hearts and love. For centuries, our culture has used the heart as the symbol of love and even of other feelings. Love songs speak of the heart. We speak of "broken hearts." We even speak of having the "heart of a lion."

We all know better. All the heart does is pump blood. This notion that the heart is the seat of love and even of the soul goes back thousands of years. William Harvey came along and proved what the heart really does, but old myths die hard. Even when we see the myths for what they are, we still cling to them.

William Harvey (1578-1657)

Gas Exchange

Storytime

William Harvey was born in Folkestone, England. Not much else is known about his childhood, although it is a good bet that his family was "upper class." Harvey went to King's School at Canterbury. When he was 16, he went to college at Cambridge and was awarded a scholarship. Even then, Harvey was interested in eventually training physicians and Cambridge had a special emphasis in that area. After graduating with a B.A. degree, he went to the most famous medical school in Europe at that time, the University of Padua in Italy. Although he had a degree from Cambridge, his most important preparation for the discoveries he would later make was the two and a half years of training he received under a tutor named Fabricius in Italy. There, he used direct observation of dissected animals to look for the truth. 

William Harvey (1578-1657)

Gas Exchange

Storytime

Harvey received his medical degree from Padua and returned to England and practiced medicine in and around London. Back in England, he quickly established himself as a physician of great competence. He also had great political connections. This was the Elizabethan age, and Harvey married the daughter of the Queen's physician. Harvey had a huge practice and was physician to many famous people, including Sir Francis Bacon and the Royal family. Harvey also realized his dream of teaching anatomy to medical students. Among the things he taught medical students was the notion that anatomy "deals with the uses and actions of the parts [of the body] by eyesight inspection and by dissection." In other words, the truth is in the body, not necessarily in the books or in what supposedly learned men tell you.

William Harvey (1578-1657)

Gas Exchange

Storytime

Harvey came along during the Renaissance, the "age of enlightenment" when thoughtful people began to challenge old myths and to explore new ways of looking at things. This fresh approach applied to medicine as well as to art and literature. The ancient belief about what the heart did was challenged by Harvey, and he devised clever ways to determine what the heart really did and how blood circulates.

In those days, medical professionals recognized that there was arterial and venous blood, but they had some primitive ideas otherwise. For example, they thought that blood originated from three places. The liver provided blood for nourishment and growth, the heart provided blood for life itself, and the brain provided blood for sensation and reason. Arterial blood was thought to be "used up," never returning to its source. These medicine men had the bizarre notion that the heart did not pump blood, but rather sucked it in like a vacuum when the heart relaxed in between contractions. Movement along the vessels was thought to result from contractions of the arteries! They did know that it took air (actually oxygen) to make arterial blood, but they thought the air was transported by the pulmonary veins into the heart. So, you can see how hard it would be to convince such people of our modern notions of blood circulation. That was the challenge that Harvey faced when he finally figured out the truth and published it in 1628.

William Harvey (1578-1657)

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Some anatomists in that era helped lay the groundwork for acceptance of Harvey's ideas. Most notable was Vesalius, who showed that the two sides of the heart were separated. Realdo Colombo worked out the connections with the lung and performed experiments showing that pumping of blood occurred when the heart contracted.

Harvey performed actual experiments on animals, first on frogs because their hearts were simpler. He noticed that so much blood left the heart in one minute that there was no way it could continually be absorbed by the body and re-made. His calculations proved that the amount of blood pumped out of the body far exceeded the total amount of blood in the body. Thus, blood HAD to circulate!

William Harvey (1578-1657)

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Of course, Harvey could not prove by direct observation how circulation continued through the organs in capillaries. But his experiments proved that there had to be very small connections between the arterial side and the venous side of an organ. One of his most famous experiments was in the human, where he put a tourniquet around the forearm. At first, the arm was tied so tight that arterial blood could not enter. The veins looked normal. When the tie was loosened enough to let arterial blood in toward the hand, yet the surface veins were still closed, the veins became swollen, showing that blood had poured into the hand and then moved back up in veins. Harvey also showed that the valves inside of veins were oriented so that they always directed blood back toward the heart.

William Harvey (1578-1657)

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Harvey published his findings in Latin in a book entitled "An Anatomical Exercise Concerning the Motion of the Heart and Blood in Animals." All learned books in that day were published in Latin. This one, interestingly, was published in Germany, not England (where he was from). In his own words, here is what Harvey gave as the reason for writing the book, "These views as usual, pleased some more, others less; some chide and calumniated me, and laid it to me as a crime that I had dared to depart from the precepts and opinions of all anatomists; others desired further explanations of the novelties, which they said were both worthy of consideration, and might perchance be found of signal use."

The book was an immediate sensation, because it so effectively challenged views that had dated back to the days of Aristotle.

William Harvey (1578-1657)

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Many people do not realize that Harvey was also a pioneer in reproductive science. He argued that humans and other mammals develop from the eggs of females that have been fertilized by sperm from males. Mammalian eggs had never been seen, and it was not until 200 years after Harvey’s work that they were seen. Harvey's line of thinking was so persuasive that this idea was immediately accepted, although no proof could be demonstrated at that time.

Harvey became a very wealthy man. Not only was his medical practice enormously successful, but he profited from the advice he got from his brothers, who were successful merchants. He gave a building and library to the College of Physicians. Unfortunately, his original manuscripts were destroyed when the building burned down in the Great Fire of London in 1666. Toward the end of his life, Harvey became a political outcast because the King he served so loyally, Charles I, had been executed in a civil war.

William Harvey (1578-1657)

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Harvey was also troubled by his enemies in the medical community. Some physicians in that day had difficulty accepting that they had been wrong. Harvey's discoveries would require them to abandon long-held views and practices or require them to construct new justification for practices that they could not give up, such as blood-letting. These people considered Harvey to be a "crackpot," and they tried to ruin his reputation. His medical practice did suffer.

Harvey did not bother to argue the matter, although he did write one rebuttal to a particularly obnoxious critic. Harvey let his observations and clear thinking stand on their own merit. Harvey prevailed, even in his own time.

References

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Curtis, R. H. (1993). Great Lives - Medicine. New York: Charles Scribner's Sons Books for Young Readers

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Harrison, W. C. (1967). Dr. William Harvey and the Discovery of Circulation. New York: MacMillan Company.

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http://www.fordham.edu/halsall/mod/1628harvey-blood.html Modern History Sourcebook: William Harvey

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https://www.williamharveyresearch.com/about-us/introduction William Harvey Medical Research Foundation 

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www.blupete.com/Literature/Biographies/Science/Harvey.htm

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Common Hazards

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Smoking

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Overview

Smoking is the leading cause of lung cancer, which causes more deaths than any other form of cancer. Smoking is linked to 80-90% of lung cancer deaths. Tobacco smoke contains a toxic mix of over 7,000 chemicals, at least 70 of which are known to cause cancer in people or animals. Smoking affects both smokers and people nearby, through second-hand smoke.

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Why is smoking hazardous?

There are three major reasons smoking is dangerous:

1. "The nicotine effect"

• Nicotine is one of the major chemical components in the tobacco leaves used to make cigarettes. Nicotine reaches the brain just a few seconds after smoking begins. The rich blood supply in the lungs picks up any chemical in the air very rapidly.
• Nicotine causes the nervous system to stimulate the release of adrenaline into the blood. When adrenaline increases in the blood, it causes the heart to beat faster, the blood vessels to constrict (to become narrower), and the breathing rate to increase. Nicotine constricts blood vessels directly, too. Constricted vessels create a large resistance for the heart to pump against. Nicotine also constricts the blood vessels in the heart and can promote heart attacks. 
• Initially nicotine gives the brain a boost, but when the effect wears off, fatigue and depression set in.
• Nicotine is one of the most addictive drugs known. Just a few puffs can create cravings for nicotine in some people. Young people are more likely to get addicted quickly than older people!

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2. Lung Irritation

In addition to nicotine, the burning of tobacco produces other hazardous materials. Some of them are:

• Acetone - a solvent, used in nail polish remover, for example.
• Carbon Monoxide - an odorless, colorless poisonous gas that is lethal in large doses. In smaller doses, carbon monoxide causes increased heart rate and shortness of breath. Carbon monoxide attaches itself to the red blood cells and blocks their ability to carry oxygen.
• Formaldehyde - a preservative for dead bodies. In cigarette smoke, this chemical is a known carcinogen and causes respiratory problems.
• Hydrogen Cyanide - short-term exposure can lead to headaches, dizziness, nausea and vomiting.
• Lead - a highly toxic metal, capable of causing serious damage to the brain, kidneys, nervous system and red blood cells.

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Cigarette smoke contains many organic tars that irritate delicate lung tissue. As the irritation increases, the lung linings begin to break down, reducing the efficiency of the lungs. One common disease resulting from the breakdown of the lung linings is emphysema.

• In emphysema, the alveoli over inflate because they are trying to let more oxygen into the blood. This over inflation reduces the elasticity of the alveoli and makes them less efficient.
• As emphysema progresses the lungs become less elastic and can no longer clear the air out of the lungs.
• When the air remains in the lungs for a longer period of time than normal, the oxygen is depleted and carbon dioxide builds up.
• When carbon dioxide builds up in the lungs, the alveoli swell and may even burst open. This causes tissue damage and can lead to scar tissue.
• The lungs do not exchange old air for new air efficiently.

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3. Lung cancer

Smoking is the leading cause of lung cancer in the United States. Lung cancer causes more deaths in the United States than any other type of cancer. For more info click here. We will discuss this in depth on the next page.

Similar problems occur with snuff and chewing tobacco. The nicotine effect is the same. The irritation and cancer effects can be the same except it is the mouth that is affected instead of the lungs.

Source: CDC

Lung Cancer

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Overview

Although lung cancer is the leading cause of cancer deaths in the United States, it is also one of the most preventable kinds of cancer. At least four out of five cases are associated with cigarette smoking. More than 228,000 people in the U.S. are diagnosed with lung cancer each year, most between the ages of 40 and 70. About 143,000 deaths are caused from lung cancer each year in the United States. Click here for more statistics.

What causes lung cancer?

Cigarette smoke has 7,000 chemicals, and of these, over 70 are known to cause cancer. Normal human cells become cancer cells when exposed to carcinogens.

The risk of developing lung cancer in humans is proportional to the number of cigarettes smoked. Smokers are 15-30 times more likely to develop lung cancer compared to people who have never smoked.

Lung Cancer

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For nonsmokers, here is a normal lung to compare to the smoker's lung below. This is what your lungs should look like.

The picture on the right is a smoker's lung. Cigarette smoke has tars and chemical agents in it that irritate the lungs and cause lung cancer to form. The cancer cells in this picture are shown by the whitish area in an otherwise blackened lung.

Source: American Lung Association

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The cost of lung cancer

The Centers for Disease Control state that the total economic cost of smoking is more than $300 billion a year. That includes nearly $170 billion in medical care for adults and more than $156 billion in lost productivity due to premature death and exposure to secondhand smoke.

Chances of survival

The lung cancer five-year survival rate is 18.6 percent, which is lower than many other leading cancer types. However, the five-year survival rate for lung cancer is 56 percent in cases when the disease is found earlier and still localized within the lungs. Unfortunately, more than half of people with lung cancer die within one year of being diagnosed.

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In its early stages, lung cancer normally has no symptoms. Most lung cancers begin to grow silently, without any symptoms. Patients with lung cancer often do not develop symptoms until the cancer is in an advanced stage. The actual time from when one cell becomes cancerous until it is large enough to be diagnosed or produce symptoms may take as long as 10 to 40 years. When symptoms start to appear, they are usually caused by blocked breathing passages or by the spread of cancer to other parts of the body. When symptoms are present, they are different in each person, but may include a cough that doesn’t go away, hoarseness, chest pain, shortness of breath, and coughing up blood.

What are the symptoms of lung cancer?

Conclusion

Smoking is the leading cause of preventable death. Smoking causes cancer. To reduce your chance of getting lung cancer by 80-90%, don’t smoke!

Secondhand Smoke

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Passive Smoking (Secondhand Smoke)

The smoke emitted from the end of a burning cigarette has double the concentration of nicotine and tar when compared to the smoke actually inhaled by the smoker (through a filter). It also contains higher amounts of cancer-causing chemicals. This is because smokers inhale smoke that is filtered through both the unburned tobacco and the filter at the end of the cigarette. This means that non-smokers subjected to secondhand smoke breathe in a more potent smoke than smokers do. Therefore, non-smokers subjected to secondhand smoke may actually suffer worse consequences than the smokers themselves.

Source: https://teens.drugabuse.gov/blog/post/are-you-secondhand-smoker

Secondhand Smoke

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Here are some of the effects of second-hand smoking:

• Lung Cancer – Long-term exposure to secondhand cigarette smoke has been shown to increase the risk of lung cancer by 20 – 30%. In fact, each year, more than 7,300 nonsmokers die of lung cancer as a direct result of passive smoking.
• Cardiovascular Disease – Secondhand smoke causes nearly 34,000 premature deaths from heart disease each year in the U.S. Nonsmokers that are exposed to secondhand smoke have a 25-30% increased risk of developing heart disease, and a 20-30% increased risk for stroke. More than 8,000 deaths from stroke each year are caused by secondhand smoke exposure.
• Children – Children who are exposed to secondhand smoke have twice the risk of being hospitalized for chest illnesses such as pneumonia and bronchitis than children not exposed to the smoke. They are also much more likely to get ear infections, tonsillitis, wheezing and childhood asthma. In fact, passive smoking in known to be one of the main contributory factors to the development of childhood asthma and has been shown to increase both the frequency and severity of the asthma attacks.

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Source: https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/health_effects/

There is not a risk-free level of exposure to secondhand smoke! To reduce the risk of secondhand smoke, parents can keep anyone from smoking in your home. Other ways to prevent exposure are to not allow anyone to smoke in the car (even with the window down) and make sure day cares and schools are smoke-free. For information for teens about secondhand smoke, click here.

Air Pollution

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Overview

Everyday hundreds of toxic chemicals are released into the environment. Many of these chemicals are hazardous to our health and cause adverse reactions. Our body has some defense against these pollutants, but it is important to remember that we should do our best to avoid them. Let's find out why.

Source: https://www.niehs.nih.gov/health/topics/agents/ozone/index.cfm

What is air pollution?

• Air pollution is a general term for a substance that contaminates the environment. For example, the exhaust emitted from cars contaminates the environment because it releases excessive amounts of ozone, carbon monoxide, nitrogen oxides, and lead.
• Pollution can come from gases, particles, or liquids. Many times, these pollutants are man-made, but sometimes they can come from the environment. For example, pollen, which is released by trees and plants, can become very abundant in the air we breathe and irritate those people who are allergic. 

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Why is air pollution so bad for your lungs?

Humans are a collection of organ systems all working together to keep the body in good working order. The body must maintain a balanced environment for the organ systems to function properly. When the body is exposed to pollutants, this balance can be disturbed. For example, when carbon monoxide, a deadly gas found in cigarette smoke and automobile exhaust, is inhaled into the lungs, it interferes with the blood’s ability to take up oxygen. Click here to see how.

• Some natural pollutants like pollen, ragweed, and molds trigger allergies in the body. Hay fever is a condition characterized by allergic reactions to these natural pollutants.
• As the body is exposed to allergens, or allergy-causing substances, it begins to build up a defense. Once the body builds up a defense against a substance, it will release defensive substances like histamine to help protect the natural balance the body needs.
• The release of histamine and other defensive substances can trigger itching, sneezing, tissue swelling, and sinus problems. While these may not be deadly, they are often inconvenient and can aggravate other conditions that may be present, like asthma.
• Asthma is a condition where allergens like pollen, dust, or other kinds of pollution can cause the airways to become narrower and reduce airflow to the blood vessels in the lungs, where gas exchange is taking place.

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How can air pollution be prevented?

• Air pollution cannot be prevented, but it can be reduced. Air pollution comes from many sources, some natural and others are man-made.
• Automobile pollution is the largest contributor to air pollution in the United States. This can be reduced by increasing the use of public transportation systems and car pools and reducing the amount of pollution vehicles cause.
• Recycling is also a great way of helping reduce pollution. Recycling means that the factories which make goods for us do not have to make as many products for us and do not create as much waste which can pollute our environment.

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Where is air pollution found the most?

Source: https://www1.nyc.gov/html/dot/html/motorist/gridlockalert.shtml

• Pollution is generally highest in large cities and industrial centers.
• Pollution from natural sources like pollen from trees is a problem in the eastern and Midwestern United States. 
• Ragweed, which is the most common cause of hay fever, is found in most parts of the United States.

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Pollution can also be an indoor problem. Some allergens like dust or cat and dog hair can build up inside homes and work places and cause extreme discomfort for individuals that are allergic to them. Another source of indoor pollution occurs from chemicals in new or remodeled buildings.

• "Sick building syndrome" is a result of the buildup of chemicals that are continuously released from new furniture, fabrics, detergents, paints, building materials.
• "Sick building syndrome" is increasing in prevalence because buildings are becoming more efficient at heating and cooling the air in a building by not circulating clean air from the outside into the building.
• As chemicals build up in a building, they can reach toxic levels and cause illness.
• "Sick building syndrome" can be avoided by maintaining a clean environment with adequate circulation of air from the outside. It is also important to store hazardous chemicals properly. Buildings should also be inspected to make sure that the building materials used are safe to live or work in. Air vents and filters must be cleaned regularly to help reduce the number of airborne pollutants.
• Click here for more info.

E-Cigarettes

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Image from CDC

Overview

An e-cigarette (electronic cigarette) is a device that heats a liquid into a vapor that can be inhaled into the lungs. This is called “vaping.” The vapor may contain nicotine (the addictive drug in tobacco), flavoring, and other chemicals. E-cigarettes can also be used to deliver marijuana or other drugs. E-cigarettes can look like regular cigarettes, pens, USB sticks, and other everyday items. Bystanders can also inhale the vapor that comes from an e-cigarette.

This Image shows some of the substances that are found in e-cigarette vapor.

Image from CDC

E-Cigarettes

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What are the dangers of E-Cigarettes?

• The vapor that is inhaled from the e-cigarette can contain toxic substances. It is common for these products to contain nicotine (highly addictive), THC (the mind-altering compound of marijuana that produces the “high”), vitamin E acetate (impairs lung function), heavy metal particles, and flavoring such as diacetyl (a chemical linked to serious lung disease), and cancer-causing agents.
• It is very difficult for the users of these e-cigarettes to know what substances they contain. The CDC has found that many e-cigarettes that are marketed as containing zero percent nicotine have been found to contain nicotine.
• E-cigarettes seem to be particularly attractive to young users. While cigarette usage in youth is on a downward trend, e-cigarette use has skyrocketed. In 2018, 3.6 million U.S. middle and high school students used e-cigarettes. In a study it was found that 37% of high school students used e-cigarettes!
• In addition to the dangers from long term use, like lung cancer, there is an alarming spike in the rate of more sudden cases of serious lung injury from the use of e-cigarettes. As of October 2019, the CDC reported more than 800 lung injury cases associated with e-cigarette use and twelve deaths had been confirmed. The CDC considers the use of e-cigarettes a “public health crisis.”

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What should you do?

The National Institute on Drug Abuse (NIDA) recommends that e-cigarettes should never be used by youths or young adults. The risk of lung disease, addiction, and serious lung damage is too great. They also state that vaping might serve as an introductory product for preteens and teens who then go on to use cigarettes or illegal drugs. Bottom line: these products are dangerous and should not be used! For more information on e-cigarettes, click here.

Activities

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Click to download an activity

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Activities

• Student Activity Sheet #1- Build Your Own Spirometer
• Student Activity Sheet #3- Blow it Up!
• Student Activity Sheet #4- Breathing Easy?

Self-Study Game

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Click to play a game

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Self-Study Game

• Quizizz

Post-Test

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Click below to take the post-test for this unit!

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• Google assessment

A-H

Glossary

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asthma - a chronic condition in which the bronchi become inflamed and swell, narrow, and produce extra mucous. This makes it difficult to breathe and can cause wheezing, coughing, and shortness of breath. Attacks can be triggered by many factors including allergens, weather, exercise, and medicines. It can usually be managed with medications to open up the airways and decrease inflammation. Return to What We Know | Return to How We Know | Return to Common Hazards

carcinogen - anything that is known to cause cancer. Return to Common Hazards

cartilaginous - composed of or relating to cartilage. Cartilage is a somewhat elastic tissue that is present in embryos but is then slowly replaced by bone as the infant grows; however, some cartilage remains, such as in your nose, respiratory passage, joints, and external ear. Return to What We Know

chronic - of long duration or frequent occurrence. Return to How We Know

circulatory system - organ system composed of the heart, arteries, capillaries, and veins. Its main functions are to transport nutrients and oxygen to cells in the body, remove waste and carbon dioxide from cells, and allow for gas exchange in the lungs. Return to What We Know

hemoglobin - a large, protein compound that carries oxygen in the blood. It is made of up four heme groups with a molecule of iron in the middle. The iron molecule gives the hemoglobin its bright red color when oxygen is attached. When oxygen is not attached, the hemoglobin changes shape and its color to a deeper bluish red tint. Return to What We Know | Return to How We Know

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Glossary

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