Which of the following physiological responses is caused by the release of antidiuretic hormone?
A.
Decrease in the concentration of calcium in the glomerulus
B.
Increase in water reabsorption in the collecting duct
C.
Increase in the concentration of calcium in the glomerulus
D.
Decrease in water reabsorption in the collecting duct
The Correct Answer and Explanation is:
The correct answer is:
B. Increase in water reabsorption in the collecting duct.
Explanation:
Antidiuretic hormone (ADH), also known as vasopressin, plays a critical role in the regulation of water balance within the body. It is released by the posterior pituitary gland in response to signals such as increased plasma osmolality (high concentration of solutes in the blood) or decreased blood volume, which may occur due to dehydration or blood loss.
Mechanism of ADH: ADH primarily acts on the kidneys, specifically targeting the collecting ducts and distal tubules of the nephrons. When ADH is released, it binds to receptors on the cells of the collecting duct, leading to the insertion of water channels known as aquaporins into the cell membranes. These aquaporins allow water to be reabsorbed from the filtrate back into the bloodstream, increasing water retention and reducing the volume of urine.
By increasing water reabsorption, ADH helps the body conserve water and maintain blood pressure and osmolarity. This response is especially important during times of dehydration, as it prevents excessive water loss, allowing the body to retain as much water as possible.
Why B is correct: Option B is correct because ADH directly increases water reabsorption in the collecting ducts of the kidneys. This physiological response helps dilute the blood by restoring water balance, thereby lowering plasma osmolarity and maintaining fluid homeostasis.
Why other options are incorrect:
- Option A and C refer to calcium concentration in the glomerulus, which is unrelated to ADH. Calcium regulation involves hormones such as parathyroid hormone and calcitonin, not ADH.
- Option D is incorrect because ADH increases, not decreases, water reabsorption in the collecting duct.
Thus, the release of ADH primarily leads to an increase in water reabsorption in the collecting duct.