| Clinical MCQs 19 :The correct answer is E. -
05-07-2006, 08:06 PM
Thats right the correct answer is E.
About 65% of the water filtered by the glomeruli (180 L/day) is reabsorbed in the proximal tubule, 15% in the loops of Henle (choice C), 10% in the distal tubules (choice B), and less than 10% in the collecting ducts (choices A and D); about 1 L of water is normally excreted as urine each day.
The amount of water reabsorbed in the proximal tubule and loop of Henle is not affected by ADH, because ADH does not affect tubular permeability in these segments of the nephron. However, ADH increases the permeability of the distal tubules and collecting duct, which increases reabsorption of water.
When ADH levels are high, the urine output can decrease to less than 0.5 L/day; when ADH levels are low, the output of urine can increase to more than 30 L/day. Even at these extremes, however, most of the water in the glomerular filtrate is still reabsorbed in the proximal tubule.
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