Physio L32 Renal Filtration- Reabsorption

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  1. Renal Functions
    • Filter waste from blood
    • Maintain blood volume
    • Maintain blood osmolarity
    • Uses: Filtration, Reabsorption, Secretion
  2. Nephron
    • Functional Unit of the kidney
    • Has vascular system and tubular system
    • All but cells and proteins in blood can be filtered
    • Most reabsorbed, remainder= urine
  3. Vascular System
    • 2 capillary systems: 1 for filtering and 1 for reabsorption
    • Afferent arteriole-> glomerus (filtration) -> efferent arteriole->peritubular capillaries (reabsorption) -> venules
  4. Tubular System
    • S- shaped
    • Bowman's Capsule (receives filtrate) -> proximal tubule -> Loop of Henle -> distal tubule -> collecting duct -> ureter
    • Variable reabsorption
    • Hormonal control of volume
    • (80% of plasma that enters the glomerus is NOT filtered and leaves through efferent arteriole; 20% DOES)
  5. Glomerular Filtration
    • From glomerulus into Bowman's capsule
    • Glomerular capillaries have very wide pores
    • Only cells and proteins are not filtered
  6. Inulin
    • Fructose polymer
    • Filtered, not reabsorbed or secreted
    • Used to measure glomerular filtration rate (GFR)
    • Inject in blood- measure in urine- proportional to amount of filtration
    • GFR ~125ml/min, 1/40 of total blood volume
  7. Hydrostatic/ Osmotic Pressures
    • Hydrostatic: BP force filtrate into Bowman's Capsule
    • Osmotic Pressures: so much fluid is filtered, remaining proteins have higher than normal osmotic pressure
    • Net: lots of filtration
  8. Control of GFR
    • Afferent arteriole radius controls entry to glomerulus
    • Afferent Arteriole dilation increases GFR
    • Afferent arteriole constriction decreases GFR
    • Sympathetic nerve constrict afferent arteriole, decreases GFR
  9. Tubular Reabsorption
    • Must recover most filtrate
    • 125 filtered ml/min reabsorbed -> 1ml/min urine, 1.44 L/day
    • 125 filtered, 123 ml/min reabsorbed -> 2ml/min urine, 2.88 L/day
    • Excess urine loss in diabetes -> decrease BP -> shock -> death
  10. Transport Maximum
    • Different carriers for different molecules
    • TM is limit of transport due to limited number of carriers
  11. Glucosuria
    • 3 times more carrier capacity than normal filtered load
    • If G in urine, blood must have at least 3 times more G than normal
  12. Sodium Reabsorption
    • Controls reabsorption of many other molecules
    • Na+ pump only on basolateral side of tubular cells
    • Pump Na+ out, create gradient for Na+ entry into cells
    • ATP needed for energy
    • Tight junctions prevent flow in spaces between cells
    • Caffeine decreases Na+ reabsorption
  13. Cotransport
    • Carries for Na+ and cotransported molecule
    • Glucose, amino acids, bicarbonate, Cl- are cotransported with Na+ during reabsorption
    • Energy use is Na+ movement down gradient into cells
    • H2O follows osmotically at proximal tube
    • Variable H2O reabsorption at distal tube an collecting duct
  14. Glucose Reabsorption
    • Binds to carrier with Na+ on luminal side to enter tubular cell
    • Separate, non-Na+ glucose carrier moves G into interstitial space
  15. Proximal Tubule Water Reabsorption
    • 60-70% water reabsorbed in proximal tubule
    • 180L/day filtered ~1L of urine, variable (distal tubule and collecting duct)
    • 500mL of urine minimum per day to remove toxins
    • Osmotic reabsorption of water follows solutes, especially Na+
Card Set
Physio L32 Renal Filtration- Reabsorption
msu physio exam
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