Question

Antidiuretic hormone promotes the retention of water by stimulating a. the active transport of water. b. the active transport of chloride. c. the active transport of sodium. d. the permeability of the collecting duct to water.

Short answer

The correct answer is \(d \text{. the permeability of the collecting duct to water.}\) Antidiuretic hormone (ADH) promotes the retention of water by increasing the permeability of the collecting duct, allowing more water to be reabsorbed through osmosis.

Step-by-step solution

Understand the function of the antidiuretic hormone (ADH)

Antidiuretic hormone, also known as vasopressin, is produced by the hypothalamus and released by the posterior pituitary gland. Its primary function is to control water balance in the body by regulating the amount of water reabsorbed by the kidneys. When the body needs to conserve water, ADH secretion is increased, and when the body needs to get rid of excess water, ADH secretion is decreased.

Identify the target site of ADH in the nephron

The nephron is the basic functional unit of the kidney that filters waste products from the blood and forms urine. The nephron is divided into several parts, including the glomerulus, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. ADH mainly acts on the collecting ducts of the nephron.

Understand the effect of ADH on the collecting duct

When ADH levels are high, it stimulates an increase in the permeability of the walls of the collecting ducts, allowing more water to be reabsorbed from the filtrate back into the bloodstream. The reabsorption occurs through the process of osmosis, a passive movement of water molecules across a semi-permeable membrane down the concentration gradient.

Determine the correct answer based on the understanding of ADH's function

Based on the information provided on ADH's function and its target site of action, ADH promotes the retention of water by: a. the active transport of water. (Incorrect, as ADH doesn't use active transport for water reabsorption.) b. the active transport of chloride. (Incorrect, as ADH doesn't directly affect chloride transport.) c. the active transport of sodium. (Incorrect, as ADH doesn't directly affect sodium transport.) d. the permeability of the collecting duct to water. (Correct, as ADH increases the permeability of the collecting duct allowing water reabsorption through osmosis.) So, the correct answer is \(d \text{. the permeability of the collecting duct to water.}\)