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The Urinary System Kidneys are essential for life on land Fluid retention Salt (electrolyte) balance Excretion of toxic wastes. Kidney is heavily vascularized Filtration Reabsorption Secretion 1000-2000L of blood flows through kidney About 180 L of filtrate produced
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The Urinary System Kidneys are essential for life on land Fluid retention Salt (electrolyte) balance Excretion of toxic wastes
Kidney is heavily vascularized Filtration Reabsorption Secretion 1000-2000L of blood flows through kidney About 180 L of filtrate produced 1.5-2L of urine actually excreted
Glomerular filtration Pores let water and small solutes through Plasma proteins are excluded by size and charge Filtrate is formed at a rapid rate Regulation of filtration rate (GFR)
Renal autoregulation to keep GFR constant, kidneys can dilate or constrict blood vessels as necessary Reabsorption- water and solutes are “put back” into the blood Glucose and salts are reabsorbed in the proximal tubule
Loop of Henle Different parts of the loop are permeable to different molecules Osmolality of tubular fluid increases as loop descends into medulla
Collecting duct has ADH receptors Duct becomes more permeable to water Water is drawn out of the tubule Diabetes insipidus- kidneys do not respond to ADH. Lots of urine is produced
Control of electrolyte and acid-base balance by the kidney Aldosterone- sodium reabsorption (and water retention); potassium secretion Aldosterone also stimulates the secretion of hydrogen ions Excessive potassium loss – hypokalemia heart and nervous dysfunction
Acid-base regulation Secretion of H+, reabsorption of bicarbonate urine usually acidic Alkalosis- H+ conserved, bicarb secreted Acidosis- reverse Also compensated by ventilation Phosphates buffer urine