Mammalian Excretory System AP Biology Unit 6

Nephrons The filtering units in the mammalian excretory system are the nephrons. Random fact: there are approximately 1 million nephrons in each kidney Slide 2 of 14

Major structures of the nephron Glomerulus Bowman’s Capsule Proximal Tubule Loop of Henle Distal Tubule Collecting Duct Slide 3 of 14

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 Slide 4 of 14

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) Slide 5 of 14

Selective Reabsorption In the proximal tubule, many useful solutes are reabsorbed back into the body fluid Glucose, amino acids, salts, some water Slide 6 of 14

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 Slide 7 of 14

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 Slide 8 of 14

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 Slide 9 of 14

Distal tubule More secretion and reabsorption takes place in the distal tubule Slide 10 of 14

Collecting Duct More water is reabsorbed in the collecting duct  urine is concentrated Pathway of urine: kidney  ureter  bladder  urethra Slide 11 of 14

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 Slide 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 Slide 13 of 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 Slide 14 of 14 