Question

This question is based on the diagram of a mammalian nephron given below.

Which is the target of ADH?

• A. A
• B. B
• C. C
• D. D

Answer 1

The correct option is D D

A - renal artery; B - proximal tubule; C - loop of Henle; D - collecting tubule. The first three steps in urine formation, filtration, reabsorption, and establishment of an osmotic gradient, result in a fluid that is slightly hypotonic to blood. The major solutes still present in this fluid are urea and other wastes. Electrolytes and water are always absorbed by the distal tubule, the amount of Na+, Cl-, and water absorbed is variable. Regulation of these processes are under hormonal control. If the Na+ levels in the blood are low, the hormone aldosterone is released. which leads to reabsorption of Na+ and Cl- in the distal tubule. Water will also flow into the tubule via osmosis. However, if a person is dehydrated, the hormone ADH (antidiuretic hormone) is released. This causes aquaporin channels to be inserted in the membrane of the collecting duct so, that large quantities of water can be reabsorbed.