Chapter 44 A Balancing Act and loss of water Osmoregulation regulates solute concentrations and balances the gain Excretion Gets rid of nitrogenous metabolites and other waste products Concept 44 1 Osmoregulation balances the uptake and loss of water and solutes Osmosis and Osmolarity Osmolarity the solute concentrations of a solution determine the movement of water across a selectively permeable membrane Isosmotic water is equal in and out Hyposmotic fat with water less solutes water flow is out Hyperosmotic Skinny with water more solutes water flow is in Land Animals water metabolically Land animals maintain water balance by eating moist food and producing Concept 44 2 Animal s nitrogenous wastes reflect its phylogeny and habitat Most animals convert ammonium to less toxic compounds prior to excretion Forms of Nitrogenous Waste Ammonia Need access to lots of water release across whole body or through gills Ammonia is converted to urea less toxic Taken to kidneys where it is excreted Urea Uric Acid Insects snails reptiles and birds Paste wastes little water Concept 44 3 Diverse excretory systems are variations on a tubular theme Excretory system regulates 1 Water 2 Ions 3 pH Excretory Process bodily fluids Key functions Most excretory systems produce urine by refining a filtrate derived from 1 Filtration 2 Re absorption of valuable solutes 3 Secretion of nonessential solutes and waste from the body fluids to the filtrate 4 Excretion Processed filtrate POOP Kidneys Excretory Organs of vertebrates function in both excretion and Each Kidneys is supplied with blood by a renal artery and drained by a Urine exits each kidney through a duct called the ureter both ureters drain into a common urinary bladder that stores urine until it is expelled through the urethra Kidneys osmoregulation renal vein The Nephron Nephron is the function unit of the vertebrate kidney it consists of a single long tubule renal tubule and a ball of capillaries called the glomerulus capillary network that is branched from the renal artery Bowman s capsule is located at the blind end of the renal tubule and surrounds and receives filtrate from the glomerulus Renal tubule extends from the Bowman s capsule into the proximal tubule loop of Henle distal tubule and collecting duct Urine formation 1 Filtration of Blood Filtrate occurs as blood pressure forces fluid from blood in the glomerulus capillaries into the lumen of the bowman s capsule Non Selective The filtrate produced in Bowman s capsule contains salts glucose amino acids vitamins nitrogenous wastes and other small molecules Cells and large molecules proteins are unable to pass though the glomerular capillary wall and are not present in filtrate 2 Reabsorption Most filtered Water ions molecules are reabsorbed from the renal tubule back into the peritubular capillaries reabsorption of water ions all amino acids and all glucose occurs in the proximal tubule Reabsorption of water occurs in the descending limp of the loop of Henle while absorption of sodium and chloride ions occurs in the ascending limb of the loop of Henle Reabsorption of water also occurs in the distal tubule and collecting duct HCO3 reabsorption in the distal tubule ADH increases H20 absorption in the distal tubule by increasing aquaporins and concentrate urine 3 Secretion Toxic substances and excess ions such as H K are secreted from the peritubular capillaries into the renal tubule H and NH3 are secreted into the proximal tubule H and K are secreted into the distal tubule Controlled movement of H ions contributes to pH regulation Urine Transport Substances that are not reabsorbed are transported into the collecting duct which leads to the interior of the Kidney Urine is hyperosmotic to body fluids lots of solutes less water Leaves Kidneys to the urinary bladder through the ureters urine is stored in the bladder
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