question_answer 26)

  We can produce a concentrated/dilute urine. This is facilitated by a special mechanism. Identify the mechanism. (a) Reabsorption from PCT (b) Reabsorption from collecting duct (c) Reabsorption/Secretion in DCT (d) Counter current mechanism in Henle's loop/vasa recta

Answer:

                (d) Counter current mechanism in Henle's loop and vasa recta helps to maintain concentration gradient in the medullary interstitum. Presence of such interstitial gradient helps an easy passage of water from the collecting tubule thereby concentrating the urine. PCT helps in maintaining pH and ionic balance of the body fluid by the secretion of  ammonia and potassium ions and reabsorbing 70-80% of electrolytes and water. Collecting duct helps in. reabsorption of water to produce concentrated urine and in maintaining osmolarity. It also plays a vital role in maintaining pH and ionic balance in blood by secreting  and  ion. DCT reabsorb and water along with, maintaining pH and sodium-potassium/ionic balance in blood by the selectively secreting hydrogen and potassium ions.