D3.3 Homeostasis
Understandings:
Continuity and change
Organisms
D3
HL
Key words:
Excretion
Osmoregulation
Ammonia
Urea
Uric acid
Cortex
Medulla
Pelvis
Nephron
Cortical
Juxtamedullary
Glomerulus
Bowman’s capsule
Afferent arteriole
Efferent arteriole
Proximal convoluted tubule
Loop of Henlé
Distal convoluted tubule
Collecting duct
Ultrafiltration
Selective reabsorption
Podocyte
Microvilli
Countercurrent multiplier
ADH
Aquaporins
Osmoreceptors
Hypothalamus
Pituitary gland
Vasoconstriction
Vasodilation
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D3.3.7—Role of the kidney in osmoregulation and excretion
The kidneys have two major roles in the body:
Excretion - removal of waste products
Osmoregulation - balance of water potential
What are the three main macromolecules in human diet?
What are the three main macromolecules in human diet?
Carbohydrates, Lipids, Proteins
How are excess molecules stored?
What are the three main macromolecules in human diet?
Carbohydrates, Lipids, Proteins
How are excess molecules stored?
Carbohydrates - glycogen or triglycerides
Lipids - triglycerides
Proteins - carbohydrates or fats + toxic ammonia!!!
Excess amino acids are broken down into ammonia.
Ammonia is toxic and is converted into either urea or uric acid.
Mammals excrete urea
Birds and reptiles excrete uric acid
Are you kid(ney)ing?
Kidneys can hold 22% of your blood at any given moment!
Around 1L of blood passes through kidneys every minute!
Kidneys filter 200L of fluid every day!
25% of oxygen absorbed through lungs is used to make ATP in the kidneys!
Three main structures of the kidney:
Cortex - Outer 1/5th of kidney - contains glomeruli
Medulla - Contains pyramids where tubules and blood vessels found
Pelvis - Where urine is collected before leaving via urethra
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Note: Renal artery should have smaller diameter than renal vein.
Nephron
Functional unit
A before E
Cortical 85%
Juxtamedullary 15%
D3.3.8—Role of the glomerulus, Bowman’s capsule and proximal convoluted tubule in excretion
How do you clean the fridge?
Ultrafiltration - take everything out of the fridge
Selective reabsorption - put back the things that you want to keep
Ultrafiltration
Glomerulus = capillary
Glomerulus + bowman’s capsule = renal corpuscle / malpighian body
A comes before E
Podocytes allow small molecules through but not larger molecules
How is a high pressure created in the glomerulus?
How is a high pressure created in the glomerulus?
Wide afferent, narrow efferent arteriole
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If the 1l of blood passes through the kidney every minute and the glomerulus filters 1/5th of the blood that passes through it. Why do we not produce more urine?
If the 1l of blood passes through the kidney every minute and the glomerulus filters 1/5th of the blood that passes through it. Why do we not produce more urine?
Around 99% of filtrate reabsorbed!
Selective reabsorption
The proximal convoluted tubule selectively reabsorbs useful substances by active transport.
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Proximal Convoluted Tubule
80% of filtrate reabsorbed
(100% glucose, 100% amino acids, 65% water, Na, K, Cl)
3Na-2K-ATPase
Microvilli increase surface area
Secondary active transport
The sodium potassium pump actively pumps sodium out of the cell.
Sodium passes passively through cotransporter down concentration gradient.
Glucose is cotransported against its concentration gradient
D3.3.9—Role of the loop of Henle
The loop of Henle maintains hypertonic conditions in the medulla.
Loop of Henle
Countercurrent multiplier
Descending vs ascending limb
The renal medulla is very salty!
The deeper into the medulla, the saltier it becomes.
Increase in osmolarity
Osmotic gradient allows reabsorption of water and concentration of urine!
Descending limb is permeable to water but impermeable to ions
Ascending limb is impermeable to water but permeable to ions
Ascending limb carries out active transport
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The more concentrated, the quicker the sodium is pumped out
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The more concentrated, the quicker the sodium is pumped out
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The more concentrated, the quicker the sodium is pumped out
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Interstitium becomes more concentrated
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Interstitium becomes more concentrated
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Interstitium becomes more concentrated
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Water moves via osmosis, increasing concentration
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Water moves via osmosis, increasing concentration
Interstitium becomes more dilute
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Filtrate at bottom of loop is now more concentrated
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Filtrate at higher concentration is able to pump even more sodium
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Filtrate at higher concentration is able to pump even more sodium
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Increasing the interstitial concentration
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Which continues along the ascending limb
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Water then moves via osmosis into the interstitium
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Water then moves via osmosis into the interstitium
Which decreases the concentration in the interstitium
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The bottom of the loop is now even more concentrated
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Continues multiplying until maximal gradient established
Summary
Ascending limb is IMPERMEABLE to water and actively transports ions OUT - increasing the osmolality of tissue fluid (decreasing osmolality of filtrate/ urine)
Descending limb is PERMEABLE to water - increasing the osmolality of the filtrate/ urine
D3.3.10—Osmoregulation by water reabsorption in the collecting ducts
ADH controls reabsorption of water in the collecting duct.
Distal convoluted tubule and collecting duct
Regulates the urine produced to maintain osmoregulation
Sodium can be actively pumped out.
ADH stimulates insertion of aquaporins into membrane increasing water reabsorption
Collecting duct
Many nephrons drain into collecting duct
The Kidneys are essential to maintain the osmotic potential of the blood
Osmoreceptors found in Hypothalamus
ADH produced by Hypothalamus (and stored in posterior pituitary gland)
_______ osmolarity of blood detected by _____________ of __________
_______osmolarity of blood detected by _____________ of __________
___ released from _______ _______
___not released from _______ _______
___ binds _______ in nephron
___ does not bind _______ in nephron
New ________ inserted into membrane of _______ _________ _____ and ________ _____
New ________ not inserted. Already present ________ in ______ _________ _____ and ________ _____ may be removed
Concentrated urine
Dilute urine
_________ in osmolarity of blood
_________ in osmolarity of blood
Normal blood osmolarity
Increased osmolarity of blood detected by osmoreceptors of hypothalamus
Decreased osmolarity of blood detected by osmoreceptors of hypothalamus
ADH released from posterior pituitary
ADH not released from posterior pituitary
ADH binds receptors in nephron
ADH does not bind receptors in nephron
New aquaporins inserted into membrane of distal convoluted tubule and collecting duct
New aquaporins not inserted and present aquaporins in distal convoluted tubule and collecting duct may be removed
Concentrated urine
Dilute urine
Decrease in osmolarity of blood
Increase in osmolarity of blood
Normal blood osmolarity
What should the kidneys do if suffering from blood loss?
What should the kidneys do if suffering from blood loss?
ADH release also affected by changes in blood pressure.
Where are these changes sensed?
What should the kidneys do if suffering from blood loss?
ADH release also affected by changes in blood pressure.
Where are these changes sensed?
Baroreceptors of aorta and carotid arteries
Clinical case
Relation between plasma arginine vasopressin (AVP) and plasma osmolality following hypertonic 5% saline infusion.
Peter H Baylis, and Tim Cheetham Arch Dis Child 1998;79:84-89
Copyright © BMJ Publishing Group Ltd & Royal College of Paediatrics and Child Health. All rights reserved.
Relation between plasma arginine vasopressin (AVP), also known as ADH, and plasma osmolality following hypertonic 5% saline infusion. The shaded area is the normal response.
Relation between urine osmolality and plasma arginine vasopressin (AVP) after a period of fluid restriction.
Peter H Baylis, and Tim Cheetham Arch Dis Child 1998;79:84-89
Copyright © BMJ Publishing Group Ltd & Royal College of Paediatrics and Child Health. All rights reserved.
Relation between urine osmolality and plasma arginine vasopressin (AVP), also known as ADH, after a period of fluid restriction. The shaded area represents the normal relation.
The length of the loop of Henle is positively correlated with the need for water conservation in animals.
D3.3.11—Changes in blood supply to organs in response to changes in activity
Can you explain this graph?
Vascular shunt mechanism
Blood flow to non essential organs will be reduced via vasoconstriction
Blood flow to essential organs will be increased via vasodilation
Can you…
Name the two main functions of the kidney?
Label both a kidney and a nephron?
Explain the processes of ultrafiltration and selective reabsorption?
Explain the role of the loop of Henle in water reabsorption?
Explain the role of ADH in osmoregulation?
Describe the changes in blood flow with different levels of activity?