Notes

Sodium and Water Reabsorption along the Nephron:
NaCl and H2O Reabsorption along the loop of Henle- thin descending limb reabsorbs water via AQP1 channels, thus NaCl conc. is higher. In thick and thin ascending limb, water is not absorbed while 25% of filtered load of NaCl is absorbed via transcellular and paracellular pathways.
Transcellular Na+ Reabsorption in TAL (Thick ascending limb):
ATPase pump causes Na+ conc. to be low in cell. NKCC2 symporter brings in sodium, 2 chloride, and potassium into the cell. K+ channels on apical side allow this pump to operate. Na-H antiporter brings sodium into the cell (dependent on protons and carboanhydrase). K-Cl symporter moves potassium out of the cell. Na-HCO3- symporter moves sodium and carbonic anhydrase out of cell. Chloride and potassium channels expressed on basolateral side, moving ions out of the cell
Paracellular Na+ Reabsorption in the cell in the TAL
Lumen positive voltage generated by K+ channels pushes cations paracellularly
Na+ Reabsorption in Early DCT:
ATPase pump maintains low Na+. NaCl enters the cell via NCC symporters. Chloride channels on basolateral side allow Cl to be reabsorbed. Diluted tubular fluid
Na+ Reabsorption in late DCT and Collecting Duct:
Depends on two kinds of cells; principal cells and intercalated cells. Principal cells reabsorb Na+, Cl-, and water and secrete K+. Intercalated cells reabsorb K+ and secrete H+ or HCO3-. Solute movement in principal cells depends on Na/K ATPase pump and H+/K+ pump in intercalated cells. Aldosterone regulated Na+ channels are expressed in late DCT and collecting duct.