24-1 e. Kidney Function (1) Glomerulus: filtration (2) PCT: tubular reabsorption (3) Loop of Henle (a) descending loop: filtrate concentrates (b) ascending loop: filtrate dilutes Constant recycling of salt creates “standing salt gradient” in kidney medulla

24-2 PCT DCT LOOP CD GLOM

NaCl H2OH2O

H2OH2O H2OH2O H2OH2O H2OH2O NaCl

NaCl

24-6 (4) Distal convoluted tubule both active absorption and secretion (a) control ion concentrations in filtrate e.g., Na +, Cl -, K +, HCO 3 -, H + regulates blood pH and ion composition (b) removes wastes from blood by secretion At end of DCT, filtrate is back to300 mosm/L

NaCl H2OH2O

24-8 (5) Collecting Duct Filtrate in CD passes down through standing salt gradient in medulla ECF Water will leave filtrate by osmosis Water picked up by blood and returned to general circulation Salts and wastes remain behind to form a concentrated urine

24-9 (6) Summary All kidneys: elimination of wastes conservation of needed salts and nutrients Looped kidneys (birds and mammals only): self generating osmotic gradient gives ability to concentrate urine massive savings of water in animals with high waste production and water loss

24-10 f. Control of kidney function Control water reabsorption in collecting duct Neurohypophysis/neural lobe arginine vasopressin (AVP) in mammals arginine vasotocin (AVT) in all others 9 amino acid peptide Control: endocrine reflex arc

24-11 Decreased Blood Pressure Increased Blood Osmolarity Aortic Baroreceptors CNS Chemoreceptors AVP RELEASE

24-12 AVP action increase permeability of cells to water via cAMP, induces production of proteins “water channels” works in kidney, bladder, skin kidney increases permeability of cells of collecting duct to water

mosm NO AVP low water permeability Large amounts of dilute urine DIURESIS HIGH AVP high water permeability H 2 O to circulation 1200 mosm Small amounts of concentrated urine ANTIDIURESIS AVP = AntiDiuretic Hormone (ADH) ECF

Bladder homeotherms storage organ for hyperosmotic urine poikilotherms epithelium is thin, contains ion pumps Na +, Cl -, pumped to blood, H 2 O follows H 2 O permeability controlled by AVT AVT increases, water uptake increases

Integument (skin) barrier to environment most vertebrates: impermeable to salts, H 2 O waxy coating, dead cells, scales, mucus amphibians: no barrier to H 2 O lose H 2 O rapidly can take up H 2 O along with ions AVT: increases skin permeability

Salt Glands marine elasmobranchs: rectal gland marine reptiles and birds: facial

24-17 All drink sea water to gain water no freshwater access high salt load no looped kidney: dilute urine Excrete salt load from salt glands concentrated saline solution excreted active transport of Na + /Cl - to outside 2-3 X osmolarity of blood plasma

Gut primary location for water and salt uptake ion pumping into animal water entry by osmosis

Gills pump ions in or out water follows by osmosis

24-20 C. Osmoregulatory Environments 1. Sea water (1000 mosm/L) Problem: if blood pOs does not equal water pOs then water and solutes will diffuse across gill 2 strategies: a. conform let blood osmolarity = environment hagfish: plasma = 1000 mosm salt sharks: plasma = 500 mosm salt, 500 mosm urea kidney must still regulate blood composition

24-21 b. Regulate at mosm/L gill in salt water: osmotic H 2 O loss from blood passive salt gain from environment response of marine fish: (1) drink sea water gain H 2 O and salt in gut (2) excrete Na +, Cl - by pumping out at gills (3) divalent ions, wastes excreted in urine

24-22 Marine fish kidney adapted to minimize water loss in urine very low glomerular filtration, down to 0 Overall strategy: gain water and salt by drinking excrete salt gained conserve water at all locations

Fresh water (<100 mosm/L) All animals regulate at mosm/L Problem diluting: lose salt, gain H 2 O at gills Solution don’t drink gain salt through diet conserve salt pump in at gills reabsorb from bladder

24-24 Freshwater fish excrete excess water at kidney adapted to maximize water loss in urine very high glomerular filtration, no loop “copious amounts of dilute urine”

24-25 Additional osmoregulatory problem disposal of nitrogenous wastes protein catabolism makes ammonia increases osmotic pressure of blood toxic

24-26 All fish ammonia highly soluble in water diffuses out of blood at gills Fish are “ammonotelic” excrete ammonia as nitrogenous waste

Terrestrial Environments a. Take up as much water as possible (1) Drink (2) Eat H 2 O trapped in food as humidity H 2 O generated by biochemical breakdown of complex nutrients “metabolic water” 60 ml H 2 O/100 g dry barley (3) Absorb: amphibian skin, bladder

24-28 b. Reduce water loss (1) Avoid hot environments (nocturnal) (2) Impermeable skin (3) Kidney Produce a concentrated urine: loop Kidney water conservation ability: U/P ratio = urine osmolarity plasma osmolarity reptiles: no loop, U/P up to 1 birds: small loop, U/P up to 6 mammals: great loop, U/P up to 25

24-29 (4) Respiratory system nasal labyrinth inhale: air warmed and humidified exhale: H 2 O condensed by cooling Respiration still primary H 2 O loss in xeric environments

24-30 (5) Nitrogenous wastes terrestrial: retain and detoxify ammonia Mesic environments: ammonia converted to urea in liver less toxic concentrated in urine “ureotelic”

24-31 Xeric environments urea still requires too much water ammonia is converted in liver to uric acid precipitates as insoluble salt after kidney “uricotelic” Huge water savings Ammonia:500 mls H 2 O to excrete 1 g N Urea:50 mls H 2 O to excrete 1 g N Uric Acid:10 mls H 2 O to excrete 1 g N

24-32 Ammonia fish aquatic amphibian larvae crocodilians Urea mesic reptiles and amphibians mammals Uric acid birds xeric reptiles and amphibians

24-33 d. Store H 2 O: amphibians store H 2 O in bladder and lymph tolerate dehydration draw water out of lymph draw water out of urine from bladder allow blood osmolarity to rise to 600