BMS 360 Lecture Notes - Distal Convoluted Tubule, Proximal Tubule, Extracellular Fluid
Document Summary
The countercurrent multiplier system concentrates solutes in urine. Example of countercurrent exchange system: a hot water pipe flowing to left. Closely adjacent and parallel is a cold water pipe flowing to the right. The hot water will warm the cold water by countercurrent heat exchange. The descending proximal and ascending distal tubules in the loop of henle is a countercurrent osmotic exchange system. The solute becomes hyperosmotic (multiplied) in the interstitial fluid of the kidney medulla. This system is cleverly controlled simply by the distribution of ion pumps and aquaporins along the tubules and ducts. Consider the long loop of the juxtamedullary nephrons. H2o flows downhill to hyperosmolar gradient in medullary interstitial fluid to vasa recta. Note: net water flux out of descending tubule until mosm gradient becomes equal in nearby interstitial fluid to that in descending tubule. Water flows downhill into interstitial fluid from the descending proximal tubule, Multiplying solutes from 300 to 1400 mosm at the hairpin.
