26 39 Reabsorption Secretion in the Collecting Duct By end of DCT 95 of solutes

26 39 reabsorption secretion in the collecting duct

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26-39 Reabsorption & Secretion in the Collecting Duct By end of DCT, 95% of solutes & water have been reabsorbed and returned to the bloodstream Cells in the collecting duct make the final adjustments principal cells reabsorb Na+ and secrete K+ intercalated cells reabsorb K+ & bicarbonate ions and secrete H+
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26-40 Actions of the Principal Cells Na+ enters principal cells through leakage channels Na+ pumps keep the concentration of Na+ in the cytosol low Cells secrete variable amounts of K+, to adjust for dietary changes in K+ intake down concentration gradient due to Na+/K+ pump Aldosterone increases Na+ and water reabsorption & K+ secretion by principal cells by stimulating the synthesis of new pumps and channels.
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26-41 Secretion of H+ and Absorption of Bicarbonate by Intercalated Cells Proton pumps (H+ATPases) secrete H+ into tubular fluid can secrete against a concentration gradient so urine can be 1000 times more acidic than blood Cl-/HCO3- antiporters move bicarbonate ions into the blood intercalated cells help regulate pH of body fluids Urine is buffered by HPO 4 2- and ammonia, both of which combine irreversibly with H+ and are excreted
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26-42 Hormonal Regulation Hormones that affect Na+, Cl- & water reabsorption and K+ secretion in the tubules angiotensin II and aldosterone decreases GFR by vasoconstricting afferent arteriole enhances absorption of Na+ promotes aldosterone production which causes principal cells to reabsorb more Na+ and Cl- and less water increases blood volume by increasing water reabsorption atrial natriuretic peptide inhibits reabsorption of Na+ and water in PCT & suppresses secretion of aldosterone & ADH increase excretion of Na+ which increases urine output and decreases blood volume
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Antidiuretic Hormone Increases water permeability of principal cells so regulates facultative water reabsorption Stimulates the insertion of aquaporin-2 channels into the membrane water molecules move more rapidly When osmolarity of plasma & interstitial fluid decreases, more ADH is secreted and facultative water reabsorption increases.
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26-44 Production of Dilute or Concentrated Urine Homeostasis of body fluids despite variable fluid intake Kidneys regulate water loss in urine ADH controls whether dilute or concentrated urine is formed if lacking, urine contains high ratio of water to solutes
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Formation of Dilute Urine Dilute = having fewer solutes than plasma (300 mOsm/liter). diabetes insipidus Filtrate and blood have equal osmolarity in PCT Water reabsorbed in thin limb, but ions reabsorbed in thick limb of loop of Henle create a filtrate more dilute than plasma can be 4x as dilute as plasma as low as 65 mOsm/liter Principal cells do not reabsorb water if ADH is low
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  • Spring '10
  • brooks
  • loop of Henle, tubular fluid

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