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10 reabsorpon in the distal tubule and collecng duct

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Unformatted text preview: ­ from the filtrate to the blood Fig 13.8 Reabsorp*on in the Loop of Henle •  Ascending limb –  impermeable to water –  Thick segment lined w/ Na + ­K+ pumps •  Descending limb –  permeable to water –  no ac*ve transport •  Medulla peritubular capillaries (vasa recta) form loops that can absorb water •  Interac*ons between ascending limb and descending limb form a countercurrent mul+plier system Fig 13.10 Reabsorp*on in the Loop of Henle •  Pumping of ions out of thick segment of ascending limb creates osmo*c gradient in inters**al fluid of the medulla –  Gradient amplified by urea being recycled between loop and collec*ng duct •  Water flows out of descending limb along this osmo*c gradient •  Water subsequently absorbed by vasa recta Figs 13.10 and 13.11 Reabsorp*on in the Loop of Henle Fluid in the tubule becomes more concentrated as it passes down descending limb –  ~1400 mOsM at the turn of the loop Removal of ions from ascending limb while water is retained causes fluid to become less concentrated in the ascending limb Fluid leaving the loop of Henle is hypotonic (~ 100 mOsM) ~20% of original glomeruluar filtrate volume reabsorbed by loop of Henle Fig 13.10 Reabsorp*on in the Distal Tubule and Collec*ng Duct •  Distal tubule –  Some water and Na+ reabsorp*on –  Water reabsorp*on variable depending on permeability of tubule walls •  Collec*ng Duct –  Conducts fluid through medulla –  Strong osmo*c gradients favor reabsorp*on of water out of duct –  Water reabsorp*on variable depending on permeability of tubule walls •  If permeable, small amount of concentrated urine produced •  If impermeable, large amount of dilute urine produced –  Some Na+ reabsorp*on Fig 13.12 Urea Contributes to Hyperosmo+c Renal Medullary Inters++um and to a Concentrated Urine Countercurrent Exchange in the Vasa Recta Preserves Hyperosmolarity of the Renal Medulla • Vasa recta vessels resemble other capillaries in their high perm...
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