PPT #9B - Reabsorption of Nutrients p 526 1 Glucose[NOT REGULATED BY KIDNEY normally regulated by endocrine and liver mechanisms and amino acids are

PPT #9B - Reabsorption of Nutrients p 526 1 Glucose[NOT...

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Reabsorption of Nutrients p. 526 2. Symport carriers in the proximal tubule transfer both Na+ and the organic molecule from the lumen into the cell (Na+ passively; organics actively via symport carrier). 3. Glucose and amino acids passively diffuse down their concentration gradients across the basolateral membrane through the interstitial fluid into the capillary plasma. A . Cl- passively reabsorbed down the electrical gradient created by the Na+ entry into the peritubular cell; Cl- passes between, not into the tubular cells and into the peritubular capillaries following Na+. 4. Not only is secondary active reabsorption of glucose and amino acids linked to the basolateral Na+/K+ pump, but passive reabsorption of: (A) Cl-, (B) H2O (Fig. 14-19 ) and (C) urea (Fig. 14-20) also depends on this active Na+ reabsorption mechanism 1. Glucose [ NOT REGULATED BY KIDNEY; normally regulated by endocrine and liver mechanisms] and amino acids are reabsorbed by Na+-dependent secondary active transport.
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Tubular cell Interstitial fluid Peritubular capillary Lumen Basolateral Na+– K+ pump Lateral space KEY = Active transport of ion against concentration gradient = Passive movement of ion down concentration gradient Glucose, AAs, water & urea p. 526 Diffusion Cl- - PROXIMAL Na+ & glucose cotransporter (SGLT) Active T Passively p. 524 p. 524
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Reabsorption- Water B. Water is passively reabsorbed throughout the tubule as it follows reabsorbed Na+. : a. 80% of the water reabsorbed is uncontrolled b. 65% is reabsorbed in the proximal tubule where Aquaporin (AQP-1) channels are always open (see next slide). c. 15% is reabsorbed from the loop of Henle d. 20% of the water reabsorbed is controlled under hormonal control of vasopressin (ADH) at the distal tubule where Aquaporin ( AQP-2 ) channels are located
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AQP-1 water channels Interstitial fluid Peritubular capillary Lumen Proximal tubular cell Osmosis Hydrostatic pressure AQP-1 water channels Osmosis Fig. 14-19, p. 527 “Leaky” tight junctions Hypertonic regions in the lateral spaces (osmotic effects) Always open: Always open:
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