Question

ADH controls water permeability of
A. Collecting tube
B. Proximal convoluted tube
C. Distal convoluted tube
D. All the above

Answer 1

Hint: We know that ADH is Anti Diuretic Hormone released by posterior pituitary. It is mainly concerned with water reabsorption mechanism and also helps in controlling the blood pressure. Diuresis means excess urine production. As the name indicates, antidiuresis which means it reduces the amount of urine being lost which in turn reduces the loss of water through urine.

Complete answer:
Let us know about the function and mechanism of the hormone. It mainly acts on the blood vessels and kidney. Now,try to remember the structure of nephrons which are the functional units of the kidney. The nephron consists of glomerulus and Bowman's capsule which further continues as PCT, Loops of Henle, DCT and collecting duct. The PCT is mainly concerned with absorption of amino acids, nutrients,ions etc. The solute concentration in the tube decreases as you move along the tube. Distal convoluted tubules further continue as collecting tubes. These two regions are mainly concerned with the water absorption which is required to produce a concentrated urine that further maintains homeostasis. Here comes the ADH, it acts on the receptors of collecting duct which reabsorbs the water and ensures to produce concentrated urine and hence is said to be controlling the water permeability.

So, the correct answer is option A.

Note:
It is also called vasopressin as it acts as vasoconstrictor which means narrowing of a blood vessel and as a result blood pressure is raised. This hormone inserts aquaporins which are nothing but the water channels into the membrane of tubules. Lack of ADH can cause increased urine production by which excess amounts of water is lost and hence said to be an important hormone.