Overview Proximal Convoluted Tubule The major function of the proximal convoluted tubule (PCT) is isosmotic reabsorption of solutes and water which is imperative for maintaining the extracellular fluid (ECF) this is accomplished by a number of co-transporters such as login to view 6 more bullets Note that the PCT can be divided into an early and late PCT Na+ is reabsorbed in both portions of the PCT but via different mechanisms early PCT login to view 3 more bullets late PCT login to view 1 more bullet There are a number of hormones that act on the PCT and they include parathyroid hormone (PTH) inhibits the Na+-phosphate co-transporter angiotensin II stimultes the Na+-H+ exchange Medications that act on this portion of the nephrone includes carbonic anhydrase inhibitors (e.g., acetazolamide) osmotic diuretics (e.g., mannitol) Thin Descending Loop of Henle The thin descending loop of Henle is permeable to water but not ions water moves out of the loop into the interstitium resulting in the tubular fluid becoming more concentrated (hyperosmotic) Thick Ascending Loop of Henle The major function of the thick ascending loop of Henle is to reabsorb NaCl without water this is accomplished by the Na+-K+-2Cl− cotransporter loop diuretics (e.g., furosemide) act on these transporters reabsorption of solutes without water makes the tubular fluid dilute (thus why this is the diluting segment) There is also paracellular reabsorption of Ca2+ and Mg2+ this is driven by the lumen-positive potential difference generated by K+ backleak Distal Convoluted Tubule and Collecting Duct The distal convoluted tubule (DCT) can be divided into an early and late DCT early DCT reabsorbs 5% of the filtered sodium via a Na+-Cl− cotransporter login to view 2 more bullets it is impermeable to water and thus dilutes the tubular fluid (thus called the cortical diluting segment) late DCT and collecting duct both of these segments of the nephron are anatomically and functionally similar there are 2 major cell types login to view 17 more bullets