What effect does antidiuretic hormone (ADH) have on the nephron?
a. It increases the water permeability of the descending limb of the loop of Henle.
b. It decreases the water permeability of the descending limb of the loop of Henle.
c. It increases the water permeability of the collecting duct.
d. It decreases the water permeability of the collecting duct.

Verified step by step guidance

1. Understand the role of antidiuretic hormone (ADH) in the body: ADH is a hormone that helps regulate water balance by increasing water reabsorption in the kidneys.
2. Identify the parts of the nephron involved in water reabsorption: The nephron includes structures such as the loop of Henle and the collecting duct, which play roles in concentrating urine and reabsorbing water.
3. Focus on the collecting duct: ADH primarily affects the collecting duct, where it increases the permeability of the duct to water, allowing more water to be reabsorbed back into the bloodstream.
4. Consider the options given: Options a and b refer to the loop of Henle, which is not the primary site of ADH action. Options c and d refer to the collecting duct, which is the correct site of ADH action.
5. Determine the correct effect of ADH: ADH increases water permeability in the collecting duct, allowing more water to be reabsorbed, which corresponds to option c.

Key Concepts

Antidiuretic Hormone (ADH)

Antidiuretic hormone (ADH), also known as vasopressin, is a hormone produced by the hypothalamus and released by the posterior pituitary gland. Its primary role is to regulate water balance in the body by controlling the amount of water reabsorbed by the kidneys. ADH increases the permeability of the kidney's collecting ducts to water, allowing more water to be reabsorbed back into the bloodstream, thus concentrating the urine and reducing urine volume.

Nephron Structure

The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine. It consists of several parts, including the glomerulus, proximal tubule, loop of Henle, distal tubule, and collecting duct. Each segment has specific functions in the process of urine formation, such as filtration, reabsorption, and secretion. Understanding the role of each part, particularly the collecting duct, is crucial for comprehending how ADH affects water reabsorption.

Water Permeability in the Collecting Duct

Water permeability in the collecting duct is a key factor in the kidney's ability to concentrate urine. Under the influence of ADH, aquaporin channels are inserted into the membrane of the collecting duct cells, increasing their permeability to water. This allows more water to be reabsorbed from the filtrate back into the bloodstream, thereby concentrating the urine and conserving water in the body. This process is essential for maintaining fluid balance and preventing dehydration.