Physiology - Renal Topic #4

  1. Loop of Henle
    • responsible for 25% of Na+, 15% of water reabsorbed by kidney
    • PROBLEM: high Na+concentration in urine (up to 1200 mM)BUT Na+/K+ATPase can only pump against a 200 mM gradient
    • SOLUTION: Loop of Henle creates an OSMOTIC GRADIENT in the kidney ISF
    • osmolarity of outer cortex is isotonic
    • inner medulla is hypertonic
    • loop structure is central to creating this gradient
  2. countercurrent multiplier effect:
    • created by combining:
    • a loop structure
    • different permeabilities to Na and water in different parts of the loop
    • Effect: osmotic gradient is multiplied
  3. parts of loop of henle
    • descending loop: permeable to water but not sodium
    • ascending loop: permeable to sodium but not water
    • Na/K ATPasepumps Na into interstitium
  4. Diuretics
    • inhibits transport of Na out of tubule
    • this retains more fluid in tubule than urine
  5. Distal Tubule / Collecting Duct
    • distal tubule fluid is hypotonic (100mOsM)
    • 20% of water, 8% of Na+, absorbed here
  6. role of Anti-diuretic Hormone (ADH) = vasopressin
    • binds to membrane receptor, ↑ cAMP
    • makes membrane permeable to water
    • promotes membrane insertion of water channels (aquaporins)
    • ADH is released from: posterior pituitary
    • osmolarity receptors located in: hypothalamus
    • release stimulated by stress
    • release inhibited by: alcohol
    • non functional in diabetes insipidus
  7. response to changes in osmolarity vs. blood pressure
  8. Urea reabsorption
    • Urea – waste product formed from Nitrogenous wastes
    • formed in: collecting duct
    • uremia = build up of too much urea
    • Cortex:
    • impermeable to urea
    • urea concentration gradually increases as water is removed
    • Medulla:
    • permeable to urea
    • some urea is transported out of CD and into ascending loop
    • effect: further water retention
    • clinical implications: helps extend life for those in cases of severe dehydration
  9. Countercurrent Exchange
    • vasa recta
    • function: reabsorbtion of Na and urea
    • rapid equilibration (exchange) of Na+, water in blood with ISF
    • loop shape ensures: further concentrate urine
Card Set
Physiology - Renal Topic #4
Topic # 4 - Adjusting Urine Concentration