PHYL2001 Lecture Notes - Lecture 13: Tubular Fluid, Peritubular Capillaries, Electrochemical Gradient
Document Summary
All plasma constituents except proteins are non-discriminately filtered proximal tubule. All constituents except plasma proteins are at the same concentration in the glomerular filtrate as in plasma. Many valuable substances need to be reabsorbed. This takes place in the tubular part of the nephron. Highly selective for required substances: 100% of sugars and 99. 5% of salts are reabsorbed into the bloodstream. Only excess amounts of required substances are not reabsorbed. Wastes are not reabsorbed and eliminated as urine. Most water (99%) is reabsorbed but some (1%) leaves as it required for keeping wastes in solution. Active reabsorption takes place if any step in the transepithelial transport of a substance requires energy, even if the four other steps are passive. With active reabsorption, net movement of the substance from the tubular lumen to the plasma occurs against an electrochemical gradient. Throughout its length, the tubule wall is one cell thick and is close to a surrounding peritubular capillary.
