CHAPTER 43 Water and Electrolyte Balance PPT Notes osmoregulation control of water solutes within cells animals must maintain water and electrolyte balance in environment 4 27 2014 environments freshwater marine terrestrial osmosis water moving down its concentration gradient how water moves by following ions water moves to area of high solute concentration less more solute osmolarity concentration of dissolved substances in a solution osmoles L water diffuses from regions of lower to higher osmolarity similar to moles but takes into account dissociated ions osmotic stress conc of dissolved substances in a cell tissue is abnormal in seawater fish loses large amts of water via osmosis electrolytes via transport out but gains electrolytes via diffusion gill tissue lower osmolarity seawater higher osmolarity in freshwater fish loses electrolytes by diffusion but gains electrolytes through active transport in gains water via osmosis in terrestrial gill tissue higher osmolarity freshwater lower osmolarity terrestrial vertebrae must replace water they lose via drinking ingestion of electrolytes in food osmoregulation occurs primarily in kidney which is responsible for water electrolyte balance excretion of nitrogenous waste biologists study organisms that cope w severe osmotic stress desert locust flour beetle insects cope via minimizing water loss from body surface carefully regulating amount of water electrolytes they excrete o o chitin tough polysaccharide present in exoskeleton of insects cuticle chitin protein in insect exoskeleton hydrophobic covered w layer of waterproof wax to minimize evaporative water loss spiracles openings in tracheal system are closed to minimize water loss from trachea rest of body covered in wax except for spiracles o Malpighian tubules excretory organ that works with hindgut butt portion of digestive tract in maintaining water electrolyte balance diffusion equilibrium established through solute diffusion along concentration gradients osmoregulators maintain balance by taking in water transporting electrolytes out i e marine bony fish osmoconformers maintain high urea content electrolytes makes blood isotonic with seawater less water loss i e cartilaginous fish passive transport diffusion down electrochemical gradient no expenditure of energy in form of ATP direct diffusion facilitated diffusion channel carrier primary active transport pump active transport occurs when ATP energy source powers movement of a solute against electrochemical gradient sodium potassium pump Na K ATPase most important type of pump in animals common molecular mechanism of salt excretion ATP used to move ions against concentration gradient once pump establishes concentration gradient enables secondary active transport contransporter sodium pumped out of cells potassium pumped in o o o sodium chloride potassium transported into cells chloride diffuses into lumen potassium diffuses to extracellular liquid in sodium diffuses into lumen out secondary active transport sympoter antiporter water balance related to excretion bc removal of waste products urine require that solutes dissolve in water ammonia nitrogenous waste removed o o o o o o o o o o o 4 27 2014 in fish diffuses across gills into water via concentration gradient in humans converted to less toxic urea and excreted in urine in birds reptiles terrestrial arthropods converted to uric acid excreted as dry paste o human waste nephron tiny tubule in kidney contributes to urine formation served by blood vessels 1 3 concentrate nitrogenous wastes create possibility for Na Cl and water to be excreted or reabsorbed by distal tubule and collecting duct 1 renal corpuscle filters blood forms pre urine made of ions nutrients wastes water 2 proximal tubule epithelial cells reabsorb nutrients vitamins ions water 3 loop of Henle makes a strong osmotic gradient in tissues outside loop osmolarity as loop descends o hypothesized by Kuhn to function as countercurrent exchanger multiplier o contains 3 distinct regions w differing water ion movement countercurrent flow of fluids osmotic gradient rather than heat exchange confirmed that osmolarity of fluid inside loop is low in cortex high in medulla strong osmolarity gradient inside outside loop gradient maintained as water leaves descending limb salt leaves ascending limb 1 descending limb passive transport highly permeable to water but impermeable to solutes 2 thin ascending limb passive transport nearly impermeable to water highly permeable to Na and Cl 3 thick ascending limb active transport nearly impermeable to water highly permeable to Na and Cl vasa recta network of blood vessels found bottom of nephron lies parallel to loop of Henle o water salt diffuse from loop and into vasa recta returning water electrolytes to body 4 distal tubule convoluted portion of nephron into which filtrate moves from loop of Henle water and sodium are reabsorbed if sodium levels are low adrenal glands release hormone aldosterone actives sodium pumps reabsorption of sodium in distal tubule saves sodium 5 collecting duct not a part of the nephron where nephron empties out leaks urea urea diffuses out of innermost section creates steep osmotic gradient of space surrounding nephron high in inner medulla low in outer medulla urine formation begins in the renal corpuscle functions as filtration device composed of glomerulus Bowman s capsule glomerulus cluster of capillaries that bring blood to nephron from renal artery Bowman s capsule region of nephron surrounding glomerulus urine selective reabsorption occurs in the proximal tubule fluid inside tubule contains water small solutes electrolytes some nutrients some waste microvilli expand surface area if dehydrated brain releases antidiuretic hormone ADH aka Vasopressin which saves water o effects epithelial cells in collecting duct ADH triggers insertion of aqua porins into apical membrane cells become more permeable to water large amounts of water reabsorbed ADH increases permeability to urea which osmolarity of surrounding fluid water loss from filtrate water leaves collecting duct passively following concentration gradient from loop of Henle ADH present collecting duct highly permeable to water water conserved urine hypertonic relative to blood results in small volume of concentrated urine ADH absent collecting duct not permeable to water few aquaporins found in collecting duct epithelium impermeable to water makes hypotonic urine results in large volume of
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