This preview shows page 1. Sign up to view the full content.
Unformatted text preview: The following mechanisms direct tubular reabsorption in the indicated regions: Active transport of Na + (in the PCT, DCT, and collecting duct). Because Na + concentration is low inside tubular cells, Na + enters the tubular cells (across the luminal membrane) by passive diffusion. At the other side of the tubule cells, the basolateral membrane bears proteins that function as sodium-potassium (Na +-K + ) pumps. These pumps use ATP to simultaneously export Na + while importing K + . Thus, Na + in the tubule cells is transported out of the cells and into the interstitial fluid by active transport. The Na + in the interstitial fluid then enters the capillaries by passive diffusion. (The K + that is transported into the cell leaks back passively into the interstitial fluid.) Symporter transport (secondary active transport) of nutrients and ions (in the PCT and...
View Full Document
- Spring '10