1. Mammalian Excretory System
AP Biology
Unit 6

2. Nephrons
The filtering units in the mammalian excretory system are the nephrons.
Random fact: there are approximately 1 million nephrons in each kidney
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3. Major structures of the nephron
Glomerulus
Bowman’s Capsule
Proximal Tubule
Loop of Henle
Distal Tubule
Collecting Duct
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4. Summary of Urine Creation
Urine is created as solutes are taken out of blood
The differences in osmolarity in the tubules and the surrounding tissues plays a role
Differences in permeability in the tubule membranes also plays a role
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5. Glomerulus & Bowman’s Capsule
Glomerulus = dense ball of capillaries
High pressure blood from arteries flows into the glomerulus
substances are filtered from the glomerulus into Bowman’s capsule due to the high pressure
Everything small enough gets across (red blood cells, proteins too big to fit through)
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6. Selective Reabsorption
In the proximal tubule, many useful solutes are reabsorbed back into the body fluid
Glucose, amino acids, salts, some water
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7. Loop of Henle
The main function of the loop of Henle is to reabsorb water from the urine
Ascending limb reabsorbs NaCl into the surrounding tissue; NOT permeable to H2O
Descending limb is permeable to H2O H2O flows out of the filtrate in this area due to osmosis (high salt concentrations all around)
Descending limb
Ascending limb
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8. Loop of Henle As NaCl is actively transported out osmolarity decreases
As H2O is reabsorbed from the filtrate, the osmolarity in the solution increases
As NaCl is actively transported out osmolarity decreases
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9. Question…
Desert animals (kangaroo rats) usually have long loops of henle, while freshwater animals (beavers) have relatively short loops of henle. How does the environment one lives in relate to the length of the loop of henle?
Loop of henle is for water reabsorption. Living in a dryer area means you need to save more water from urine  need a longer loop to do this
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10. Distal tubule
More secretion and reabsorption takes place in the distal tubule
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11. Collecting Duct
More water is reabsorbed in the collecting duct  urine is concentrated
Pathway of urine: kidney  ureter  bladder  urethra
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12. Control of Excretion Processes
Antidiuretic hormone (ADH) increases the permeability of the collecting ducts to increase the reabsorption of water
Urine is concentrated further
Another name for ADH is vasopressin
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13. Control of Excretory Processes
Aldosterone also increases salt and water reabsorption in the distal tubule
Usually a response to low blood pressure/volume
The last step in a series of reactions
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14. Interfering with ADH Caffeine and alcohol are diuretics
substances that cause an individual to pee more
Caffeine and alcohol interfere with the actions of ADH  more urine produced
Alcohol = prevents ADH from being secreted
Caffeine = prevents ADH from binding to receptors on collecting duct
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