Which of the following physiological responses is caused by the release of antidiuretic hormone?
A.
Increase in the concentration of calcium in the glomerulus.
B.
Increase in water reabsorption in the collecting duct.
C.
Decrease 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, is a crucial hormone produced by the hypothalamus and stored in the posterior pituitary gland. Its primary function is to regulate the body’s water balance and osmolarity. When released into the bloodstream, ADH acts mainly on the kidneys, specifically targeting the collecting ducts and distal convoluted tubules.
Upon its release, ADH binds to specific receptors (V2 receptors) on the cells of the collecting duct. This binding triggers a series of intracellular events that lead to the insertion of aquaporin-2 channels into the luminal membrane of these cells. Aquaporins are specialized water channels that facilitate the passive movement of water across cell membranes.
As a result of this process, the permeability of the collecting duct to water significantly increases. Consequently, more water is reabsorbed from the urine back into the bloodstream, leading to a concentrated urine output and a decrease in urine volume. This mechanism is particularly important during conditions of dehydration or when the body needs to conserve water, such as in states of high plasma osmolarity.
The other options can be ruled out based on their physiological implications:
- A. Increase in the concentration of calcium in the glomerulus and C. Decrease in the concentration of calcium in the glomerulus do not directly relate to the action of ADH. Calcium levels in the glomerulus are primarily influenced by other hormones such as parathyroid hormone.
- D. Decrease in water reabsorption in the collecting duct is the opposite of what occurs with ADH action, as ADH specifically functions to increase water reabsorption.
In summary, the release of antidiuretic hormone is pivotal for enhancing water reabsorption in the kidneys, ensuring the body maintains proper hydration and electrolyte balance.