1224_Day23_Lecture (1) - Reabsorption and Secretion...

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Unformatted text preview: Reabsorption and Secretion Reabsorption – Reclaims materials – Nephron → Peritubular capillaries Secretion – – Removes materials Peritubular capillaries → Nephron Maintains Homeostasis! Mechanisms of Reabsorption Transcellular vs Paracellular Methods – Primary active transport Sodium-potassium pump – Secondary active transport Indirectly by ion gradients SGLT Solvent drag Water follows salt Proximal Convoluted Tubule Reabsorbs – – – – – – – most tubular fluid All glucose, lactate, and amino acids 65-70% of sodium 65-70% of water 90% of bicarbonate 50% of chloride 90% of potassium Most of other electrolytes Sodium Reabsorption Tubule → tubule cell: – Facilitated diffusion: Symport with Glucose, AA, phosphate, lactate Antiport with H+ Into ECF: – Antiport with Na-K pump Into peritubular capillary: – Solvent drag Chloride Reabsorption Into tubule cell: – Antiport exchange (sodium) Into ECF: – Symport (K+ - Cl-) Into peritubular capillary: – Solvent drag Glucose Reabsorption No concentration gradient Tubule → tubule cell: – Use SGLT Into ECF: – Facilitated diffusion Into peritubular capillaries – Solvent drag Transport Maximum Limited number of protein carriers – Number specific to material carried Reflects number of carriers in renal tubules available – No carrier available solute remains Appears as part of urine Other Solute Reabsorption Bicarbonate Electrolytes – K+, Mg+2, PO4-3 diffuse with water Nitrogenous wastes – Urea Organic Solutes – Lactate, amino acids, peptide hormones Tubular Secretion in PCT Waste blood Removal from – Urea, uric acid, bile acids, ammonia, catecholamines, creatinine – Penicillin, pollutants, morphine, aspirin Acid-Base Balance – Hydrogen Loop of Henle Primary purpose – Enables collecting duct to concentrate urine and conserve water Permeability characteristics – Thin segment water can leave tubule – Thick segment impermeable to water DCT and Collecting Duct Tubular fluid contains about 20% of water and 10% salts from original filtrate Would account for ~ 36 L/day of urine Aldosterone and DCT/CD “Salt-retaining hormone” Released in response to: – Decreased blood volume and BP – low Na concentration or high K+ concentration – stimulating renin-angiotensin mechanism Actions – Increases Na+ reabsorption – Reduces urine volume ANP and DCT/CD Atrial Natriuretic Peptide – Secreted by cells in atrial myocardium – Stimulated by ↑ BP or ↑ blood volume Actions – Dilation of AA and constriction of EA Increases GFR – Inhibits ADH – Inhibits Na+ and water reabsorption ADH and PTH on DCT/CD Antidiuretic hormone – Increases permeability of CD Parathyroid hormone – Promotes Ca+2 reabsorption in loop and DCT Water Conservation Collecting Duct – Reabsorbs water – Creates hypertonic (concentrated) urine Favors water reabsorption Countercurrent Multiplier Flow of tubular fluid through nephron loop – Maintains osmotic gradient Countercurrent Exchange Relationship of nephron loop, CD, and vasa recta – – Maintains hypertonic environment of renal medulla Movement of NaCl, urea, and water in each structure ...
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  • Spring '17
  • Nephron, loop of Henle, tubule

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