Animal Physiology – Osmoregulation & Excretion (Lecture Version) Chapter 44

Slide 2 of 20 Osmoregulation  Def – MGT of body’s water & solute concentration  Osmoregulation depends on the environment the organisms lives in  Marine Vertebrates (Fish) – face dehydration pressures from the sea (salt H2O)  Hypertonic solution = H 2 O exits fish cells, then  Water loss through gills or skin  To prevent desiccation:  Decreased urine production & consumption of large amounts of sea H 2 O  Active transport of salts out of body

Slide 3 of 20 Osmoregulation (Page 2)  Freshwater vertebrates (fish)  Environment is hypotonic, so need to counter osmotic pressure  Active transport of salts into body  Excrete substantial amounts of dilute urine

Slide 4 of 20 Excretion  Def – removal of metabolic wastes  Wastes include:  CO 2 & H 2 O (Respiration wastes)  Nitrogenous waste (from protein metabolism)  Ammonia, urea, or uric acid  Excretion Organs (Humans)  Skin, lungs, kidneys, & liver (site of urea production)

Slide 5 of 20 Nitrogenous Wastes  Ammonia  Highly toxic, but water soluble  Generally excreted by waterborne organisms  Urea  Not as toxic as ammonia  Humans & Earthworms excrete  In mammals, ammonia is decomposed into urea in liver  Uric Acid  Pastelike substance that you have seen on the outside of your car  NOT water soluble; Least toxic form  Deposited by birds (and reptiles) – minimum of H2O loss

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Slide 7 of 20 Urine Production in 4 Easy Steps  1. Filtration  Pressure-filtering of body fluids  Removal of water & solutes  Cells, proteins, & large particles remain  2. Reabsorption  Reclaims valuable substances from the filtrate  Glucose, vitamins, & hormones  3. Secretion  Adds other substances (toxins & excess ions) to the filtrate  4. Excretion  Altered filtrate leaves the body

Slide 8 of 20 Human Kidney  Humans need to conserve water, but also remove toxins  Kidney adjusts volume & concentration of urine due to animal’s intake of water & salt  Fluid intake is high & salt intake low = dilute (hyposmotic) urine  Fluid intake low & salt intake high = concentrated (hyperosmotic) urine

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Slide 10 of 20 Nephron

Slide 11 of 20 The Nephron  Functional unit of the kidney  Each kidney contains ~1 million nephrons  Blood:  Renal artery  (afferent & efferent) aterioles  peritubular capillaries  renal vein  Filtrate (urine):  Glomerulus OR tubule OR Loop of Henle  ureters  Bladder  urethra

Slide 12 of 20 Nephron Videos / Animations

Slide 13 of 20 6 Main Steps in the Nephron 1. Filtration from glomerulus in Bowman’s Capsule 2. Proximal (near) tubule – secretion & reabsorption  Changes the volume & composition of the filtrate 3. Descending Loop of Henle – reabsorption of H 2 O continues 4. Ascending Loop of Henle – Reabsorption of salt (NaCl) w/o giving up H 2 O = dilution of urine 5. Distal (far) tubule – K + and NaCl levels are regulated 6. Collecting Duct – filtrate becomes more concentrated as more water is reabsorbed

Slide 14 of 20 Nephron Steps  Filtration  Passive (diffusion) & nonselective  Blood pressure forces fluid from the glomerulus into the Bowman’s Capsule  Bowman’s Capsule contains specialized cells which increase the rate of filtration  Anything small enough to filter out does so  Glucose, salts, vitamins, wastes such as urea, other small molecules  Secretion  Active & Selective  Uptake of molecules that did not get filtered into Bowman’s Capsule  Occurs in Proximal tubule

Slide 15 of 20 Nephron Steps (Page 2)  Reabsorption  Water & solutes (glucose, amino acids, & vitamins) that entered the tubule during filtration are returned to peritubular capillaries then to the body  Proximal tubule, Loop of Henle, and to collecting tubule Excretion  Removal of metabolic wastes (nitrogenous wastes)  Everything that passed into the collecting tubule is excreted from the body

Slide 16 of 20 Nephron (Page 3) Loop of Henle – Acts as a countercurrent exchange mechanism  Maintains a steep salt gradient surrounding the loop  This gradient ensures that water will continue flowing out of collecting tubule of the nephron  Creates hypertonic urine  Conserves water  Longer Loop of Henle = More water reabsorption

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Slide 18 of 20 Hormonal Control of Kidneys  Under the control of Nervous & Endocrine systems  Hence, kidney can quickly respond to the changing requirements of the body  ADH (Anti-Diuretic Hormone)  Produced by the hypothalamus  Stored in the Posterior Pituitary  Targets the collecting tubule of the nephron  Hypothalamus has osmoreceptor cells that monitor blood concentrations of salts  On a feedback loop to maintain homeostasis of fluid concentration

Slide 19 of 20 Work  When body’s salt concentration is too HIGH, ADH is released into the blood  ADH increases permeability of the collecting tubule  So more water is collected from the urine, and urine volume is decreased  When body’s salt concentration is too LOW (dilute), due to water intake being too high or salt intake too low, ADH is reduced = more urine production  EtOH = ADH inhibition = excessive urine production  May lead to dehydration

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