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Tubular Reabsorption , Sodium and Water Reabsorption

Tubular Reabsorption , Sodium and Water Reabsorption. Created by David Sunwoo, not Joy Kim, F Block. Tubular Reabsorption. The process by which filtered substances are returned to the bloodstream.

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Tubular Reabsorption , Sodium and Water Reabsorption

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  1. Tubular Reabsorption, Sodium and Water Reabsorption Created by David Sunwoo, not Joy Kim, F Block

  2. Tubular Reabsorption • The process by which filtered substances are returned to the bloodstream. • Transported out of the tubular fluid -> through the epithelium of the renal tubule -> interstitial fluid -> substance diffuses into the peritubular capillaries -> internal environment • In this process, substances must first cross the cell membrane facing the interstitial fluid.

  3. Tubular Reabsorption cont.. • Tubular reabsorption mainly takes place in the proximal convoluted portion. • Microvilli is microscopic projects that form a “brush border” on the epithelial cell’s surface. • Also greatly increases the surface area exposed to glomerular filtrate • Enhances reabsorption

  4. Active Transport • Reabsorbs glucose through the walls of the proximal convoluted tubule • Utilizes carrier molecules in cell membranes • These carriers transport certain molecules across the membrane release them and the repeat the process • But has limited transport capacity – can only transport a certain number of molecules in a given time because the number of carriers is limited

  5. Tubular Reabsorption cont.. • Some glucose remains in the tubular fluid because of the renal plasma threshold (when the plasma glucose concentration increases to a critical level) • Amino acids enter the glomerular filtrate (nearly free of protein) and are reabsorbed in the proximal convoluted tubule leaving only a trace of amino acids • Lastly, the epithelium of the proximal convoluted tubule reabsorbs other substances

  6. Sodium and Water Reabsorption • Water reabsorption occurs passively by osmosis in the proximal convoluted tubule • Active transport reabsorbs most of the sodium ions in the proximal segment of the renal tubule • Negatively charged ions move during active transport through a form of passive transport • As active transport occurs, the concentration of solutes within the peritubular blood increases.

  7. Sodium and Water Reabsorption • Water moves by osmosis from the renal tubule -> peritubular capillary • Movement of solutes and water = reduction of fluid volume within the renal tubule • In conclusion, almost all the sodium ions and water that enter the renal tubule as part of the glomerular filtrate are reabsorbed before urine is excreted.

  8. Review Questions • 1. How does water move from the renal tubule into the peritubular capillary? • 2. What are microvilli and what are their functions? • 3. What’s active transport’s main job in sodium and water reabsorption? • 4. What is renal plasma threshold? • 5. Where does tubular reabsorption mainly take place in?

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