A 22-year old woman runs a 10-kilometer race on a hot day and becomes dehydrated. Assuming that her ADH levels are high and that kidneys are functioning normally, in which part of the renal tubule is most water reabsorbed?
PCT is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption. Nearly all of the essential nutrients and 70-80 percent of electrolytes and water are reabsorbed by this segment.
ADH primarily affects the ability of the kidney to reabsorb water; when present, ADH induces expression of water transport proteins in the late distal tubule and collecting duct to increase water reabsorption. This reabsorption is very less compared to the reabsorption in the proximal convoluted tubule. So eventhough the ADH level is high, proximal tubule is the part where most water is reabsorbed.