True regarding water absorption in tubules:September 2007: (A) Majority of facultative reabsorption occurs in proximal tubule, (B) Bulk of water reabsorption occurs secondary to sodium absorption, (C) 25% of water is reabsorbed irrespective of water balance, (D) Obligatory reabsorption is ADH dependent
Answer is B. Ans. B: Bulk of water reabsorption occurs secondary to sodium absorptionWater reabsorption keeps pace with the sodium reabsorption in the proximal tubules and hence the concentration of sodium and total osmolarity remains the same.