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Fluid Balance/ Nitrogen Excretion Kidney Function Salt/Water Balance • ionic composition of cytosol is maintained by osmotic interaction with intercellular fluid • intercellular fluid is conditioned by osmotic interaction with capillary contents • excretory organs control the osmotic composition of blood – differentially excrete different compounds – excrete nitrogenous wastes from terrestrial animals Salt/Water Balance • common mechanisms of excretory organs – filtration • movement of water and solutes out of capillary under pressure – secretion • active transport of additional molecules into filtrate – resorption • active uptake of solutes from filtrate Salt/Water Balance • diverse challenges of different environments – osmotic potentials of aquatic environments vary dramatically • marine: 1070 mosmol/L • fresh water: 1-10 mosmol/L – physiological responses to different environmental osmolarities vary Salt/Water Balance • physiological responses to different environmental osmolarities – osmoconformers do not regulate tissue fluid osmolarity • ionic conformers –same ionic composition as ambient • ionic regulators –modify ionic composition but not overall osmolarity Salt/Water Balance • physiological responses to different environmental osmolarities – osmoregulators maintain tissue fluid osmolarity different from environmental • hypotonic osmoregulators –marine organisms –excrete salt; conserve water • hypertonic osmoregulators –fresh water organisms –excrete water; conserve salt three osmoregulatory modes Figure 51.1 Salt/Water Balance • physiological responses to different environmental osmolarities – terrestrial organisms conserve water & salt Nitrogenous Wastes are Excreted • catabolism of amino acids & nucleotides produces nitrogenous waste – ammonia (NH3) is quite toxic • ammonotelic organisms lose NH3 to aqueous environment across gills • ureotelic organisms convert NH3 to urea –highly water soluble • uricotelic organisms covert NH3 to uric acid –slightly water soluble Three N Excretion Forms Figure 51.3 Invertebrate Excretory Systems • protonephridia – in flatworms – flame cell + tubule • tissue fluid enters flame cell lumen • cilia drive fluid toward excretory pore • tubule cells modify fluid composition • urine is less concentrated than tissue fluid protonephridia in Planaria Figure 51.4 Invertebrate Excretory Systems • metanephridia – annelid worms • fluid-filled coelom in each body segment • closed circulatory system –filtration from blood into coelom –diffusion of waste products into coelom circulatory/excretory interaction in earthworm Figure 51.5 Invertebrate Excretory Systems • metanephridia – annelid worms • metanephridia occupy adjacent segments –nephrostome collects coelomic fluid –tubule travels to adjacent segment –tubule cells resorb & secrete compounds –dilute urine leaves a nephridiopore Invertebrate Excretory Systems • Malpighian tubules - insects – join gut between midgut & hindgut – extend into body tissues – actively transport uric acid, K+, Na+ from hemolymph – take water into tubules by osmosis – muscular contractions propel toward gut – hindgut returns Na+, K+ to tissue fluid; water follows – uric acid precipitates in rectum Malpighian tubule Figure 51.6 Vertebrate Excretory Systems • nephron (functional unit of kidney) – an afferent arteriole branches into a dense capillary bed = the glomerulus – the glomerulus is surrounded by Bowman’s capsule (= renal corpuscle) – blood is filtered from the glomerulus through podocyte “fingers” into Bowman’s capsule nephron anatomy Figure 51/8 renal filtration Figure 51.7 Vertebrate Excretory Systems • nephron – glomerular capillaries combine into an efferent arteriole – the efferent arteriole branches into a peritubular capillary bed – the renal tubule modifies fluid composition • resorption & secretion – peritubular capillaries • deliver materials to be secreted into urine • take up resorbed materials tubular modification of fluid contents Figure 51.7 Vertebrate Excretory Systems • nephron – peritubular capillaries combines into a renal venule – the renal tubule delivers urine to a collecting duct fluid collection Figure 51.7 vertebrate nephron Figure 51/7 Vertebrate Excretory Systems • nephrons of different vertebrates accomplish different tasks – water excretion; salt conservation – water conservation; salt excretion Vertebrate Excretory Systems • marine bony fishes – secrete salts; conserve water • hypotonic osmoregulation • fewer glomeruli - limits volume of urine • excrete Na+, Cl-, NH3, through renal tubules & gills • do not absorb some ions from gut Vertebrate Excretory Systems • cartilaginous fishes – ionic regulating osmoconformers • N waste retained as urea • special salt-secreting sites remove excess dietary NaCl Vertebrate Excretory Systems • amphibians – conserve salt; excrete water, OR – conserve both • reduce skin permeability • estivate during hot dry periods Vertebrate Excretory Systems • reptiles & birds – conserve water & salt • minimize skin evaporation • limit water loss by excreting uric acid Vertebrate Excretory Systems • mammals – conserve water, regulate ions • excrete urine hypertonic to tissue fluids • kidney concentrates urine human urinary system; kidney anatomy Figure 51.9 human kidney • nephron components & arrangement - tubule – Bowman’s capsule - cortex – proximal convoluted tubule - cortex – loop of Henle - descending/ascending in medulla – distal convoluted tubule - cortex – collecting duct - cortex => medulla renal pyramid Figure 51.9 human kidney • nephron components & arrangement - vessels – afferent arteriole supplies glomerulus – efferent arteriole branches into peritubular capillaries – vasa recta capillary bed parallels loop of Henle – peritubular capillaries join to form the venule that empties into the renal vein – ~98% of filtrate leaves kidney in renal vein human kidney • nephron function – glomerulus filters plasma into Bowman’s capsule – proximal convoluted tubule transports Na+, glucose, amino acids, etc. into tissue fluid – water moves out of tubule by osmosis – peritubular venous capillaries take up water and molecules – tubule contents enter loop of Henle at an osmotic potential similar to plasma human kidney • nephron function – urine concentration in loop of Henle • thin descending limb –permeable to water –impermeable to Na+, Cl- thin descending limb loses water, retains NaCl Figure 51.10 thin ascending limb loses NaCl, retains water Figure 51.10 human kidney • nephron function – urine concentration in loop of Henle • thin descending limb • thin ascending limb • thick ascending limb –impermeable to water –actively transports Cl- out, Na+ follows thick ascending limb pumps out NaCl, retains water Figure 51.10 human kidney • nephron function – thick ascending limb increases solute in tissue fluid – thin ascending limb increases solute in tissue fluid – thin descending limb contents become increasingly concentrated – dilute fluid enters distal convoluted tubule – osmosis empties distal convoluted tubule until osmotic potential is same as plasma human kidney • nephron function – the loop of Henle creates a concentration gradient in the medulla – vasa recta removes water from medulla – collecting duct passes through the medulla • water leaves the duct by osmosis • highly concentrated urine is produced nephron function in the human kidney Figure 51.10 nephron function • blood plasma is filtered into tubule • ions are actively resorbed • a concentration gradient is established in the medulla • water is reclaimed by osmosis Control & Regulation of Kidney Function • Glomerular Filtration Rate depends on blood pressure and blood volume • autoregulatory renal responses – reduced blood pressure causes afferent arteriole dilation – continued low GFR causes release of renin which activates circulating angiotensin Control & Regulation of Kidney Function • autoregulatory renal responses – continued low GFR causes release of renin which activates circulating angiotensin • efferent arteriole constriction • systemic peripheral vessel constriction • release of aldosterone from adrenal cortex –stimulates Na+ resorption ( & so H2O) –stimulates thirst Control & Regulation of Kidney Function • Glomerular Filtration Rate depends on blood pressure and blood volume • antidiuretic hormone (ADH) control – ADH release increases as aortic stretch signals decrease or as osmolarity increases • increases permeability of collecting ducts to water • increases blood volume • decreases osmolarity control & regulation of kidney function Figure 51/14