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The Urinary System Kidneys are essential for life on land Fluid retention

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

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  1. The Urinary System Kidneys are essential for life on land Fluid retention Salt (electrolyte) balance Excretion of toxic wastes

  2. 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

  3. ‘’

  4. Glomerular filtration • Pores let water and small solutes through • Plasma proteins are excluded by size and charge • Filtrate is formed rapidly • Autoregulation keeps GFR constant

  5. Water and solutes are put back into blood

  6. Loop of Henle Different parts of the loop are permeable to different molecules Osmolality of tubular fluid increases as loop descends into medulla

  7. Countercurrent multiplier system • Positive feedback • High NaCl in tissue draws water out of nephron • NaCl in filtrate pumped out into tissue • Renal medulla becomes hypertonic (urea too) • Draws water out of collecting duct

  8. ADH promotes production of aquaporins Review fig. 17.21

  9. OATs secrete “foreign” substances

  10. 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

  11. Potassium is reabsorbed and secreted • Na reabsorption and K secretion regulated by aldosterone • Some diuretics can promote excess K loss (hypokalemia)

  12. The juxtaglomerular apparatus and Na regulation

  13. 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 (since bicarb is reasborbed)

  14. Na, K, and H • Plasma pH and K levels affect each other • Na is reabsorbed, K and/or H are secreted • Acidosis: H is secreted, but not K • Alkalosis: K is secreted • Hyperkalemia: K is secreted but not H

  15. Summary • Cortex and medulla; functional unit is nephron • Major functions are filtration, reabsorption, and secretion • Filtraiton rate is regulated by SNS and intrinsic mechanisms • Reabsorption of salt and water varies around nephron and is highly regulated • Nephrons reabsorb bicarbonate and secrete H • Aldosterone is critical to electrolyte balance

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