Lecture 2 Renal

Lecture 2 Renal - NPB113 Renal 2-1 Tubular Handling of the...

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1 March 2, 2010 NPB113 Renal 2-1 Tubular Handling of the Filtrate Rebsorption by Epithelial Cells and Secretion Across Epithelial Cells Driven by NA/K ATP transport in their Basolateral Membranes Overview of handling of the Glomerular Filtrate and Tubular Fluid by the Nephrons Proximal Tubule 1. 85% of the total GFR reabsorbed, including water, HCO3-, Na and other electrolytes, glucose and other sugars, Amino Acids, Small Proteins. 2. Secretion of H+ into the tubular fluid. Loops of Henle 1. Reabsorption of approximately 15% of filtered water 2. Secretion of H+ using Na+ - H+ antiporter. 3. Reabsorption ~ 25% of the filtered NaCl, K, Ca & HCO3- (and water) reabsorbed in Loop of Henle. 4. Reabsorption Na and urea in Loop of Henle (Countercurrent Multiplier System) sets up osmotic gradient for reabsorption and cycling of urea, and the reabsorption of water from late distal tubules and collecting ducts. Distal Tubules and Collecting Ducts 1. Reabsorption and secretion of Na and K fine tuned through the action of Aldosterone. 2. Reabsorption of water to maintain osmolality through action of ADH and volume regulation the cycling of Urea and Aldosterone mediated reabsorption of Na. Nephrons secrete and excrete H+ - only system capable of excreting H+ in without loss of buffer base. Some solutes move bidirectionally across epithelial cells of tubules , ie. they are both secreted and reabsorbed, - Na, K, and urea.
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2 March 2, 2010 NPB113 Renal 2-2 Tubular Handling of the Filtrate Overview of handling of the Glomerular Filtrate and Tubular Fluid by the Nephrons, cont. Reabsorption – movement of substances from tubular lumen either between (solvent drag or bulk flow) or through epithelial cells of the tubules into the peritubular space and then into the peritubular capillaries. Reabsorption can be 1. Transcellular 2. Paracellular
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3 March 2, 2010 NPB113 Renal 2-3 Tubular Handling of the Filtrate Modes of Epithelial Transport 1. Simple Diffusion 2. Facilitated Diffusion – tranporter or carrier mediated diffusion. 3. Solvent Drag or Bulk Flow movement of water, the solvent, carries solute – occurs at sites where permeability of the membrane or tight junctions is high. 4. Active Transport – symporters or antiporters Primary – ATP directly expended. Na/K exchanger Secondary Active Transport Na – Glucose, AA, Phosphate, Sulfate symporter Na – H antiporter 5. Pinocytosis – vesicular transport requires energy. Basolateral Na/K ATP pump establishes the electrochemical gradient for reabsorption and secretion of charged solutes.
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4 March 2, 2010 NPB113 Renal 2-4 Tubular Handling of the Filtrate Properties of Carrier Mediated Transport (primary & secondary active transport, symporter or antiporter facilitated diffusion) 1. Exhibits Saturation Kinetics – as transport sites become saturated, transport rate increases at slower rate reaching a maximal level once all sites are saturated. 2.
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Lecture 2 Renal - NPB113 Renal 2-1 Tubular Handling of the...

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