Mammalian Excretory SystemMammalian Excretory System

AP BiologyUnit 6

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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Major structures of the nephron

• Glomerulus

• Bowman’s Capsule

• Proximal Tubule

• Loop of Henle

• Distal Tubule

• Collecting Duct

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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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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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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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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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Loop of Henle

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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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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Distal tubule

• More secretion and reabsorption takes place in the distal tubule

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Collecting Duct

• More water is reabsorbed in the collecting duct urine is concentrated

• Pathway of urine: kidney ureter bladder urethra

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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

vasopressinSlide 12 of 14

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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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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