Question

Anti Diuretic Hormone controls water permeability of

• A. Collecting tube (distal part)
• B. Proximal convoluted tubule
• C. Distal convoluted tubule (distal part)
• D. Both A and C

Answer 1

The correct option is D Both A and C

The amount of urine produced depends on the bodys need to retain or rid itself of water. When fluid intake is low, the body begins to dehydrate, and the blood volume decreases. As blood volume decreases, the concentration of salts dissolved in the blood becomes greater, causing an increase in osmotic pressure. Osmoreceptors in the hypothalamus are sensitive to this osmotic change. They signal the posterior lobe of the pituitary gland to release antidiuretic hormone (ADH). This hormone is actually produced in the hypothalamus but is stored in the posterior pituitary and released as needed. A thirst center in the hypothalamus also responds to dehydration, stimulating an increase in fluid intake. ADH makes the collecting ducts more permeable to water so that more water is reabsorbed. As a result, a small volume of concentrated urine is produced. ADH acts on aquaporin-2, a membrane protein that forms gated water channels in the wall of the collecting ducts. These channels allow water to pass rapidly through the plasma membrane.