1. What is the response of cells in the collecting tubules in the nephrons when antidiuretic hormone AHD is secreted?
a. The tubules become impermeable to water
b. Serum potassium retention increases
c. Large quantities of dilute urine are formed
d. Water is reabsorbed from the urinary filtrate
d?
The correct answer is d. When antidiuretic hormone (ADH) is secreted, the response of cells in the collecting tubules of the nephrons is that water is reabsorbed from the urinary filtrate.
To arrive at this answer, we need to understand the role of ADH in the kidneys. ADH, also known as vasopressin, is a hormone produced by the hypothalamus and released by the posterior pituitary gland. Its primary function is to regulate the body's water balance by controlling the reabsorption of water in the kidneys.
Here's how ADH works in the collecting tubules of the nephrons:
1. In the absence of ADH: Normally, the collecting tubules are relatively impermeable to water, resulting in the production of dilute urine. This occurs because the permeability of the tubules to water is regulated by tiny pores called aquaporins, which allow water to pass through the tubule walls and be reabsorbed into the bloodstream. Without ADH, these aquaporins are not present on the surface of the tubule cells, limiting water reabsorption.
2. When ADH is secreted: Whenever there is a need for water conservation, such as during dehydration or low blood volume, ADH is secreted. ADH acts on the collecting tubules by causing the insertion of aquaporins into the tubule walls. These aquaporins allow water to pass through the tubule cells and be reabsorbed into the surrounding capillaries. As a result, more water is reabsorbed from the urinary filtrate, leading to a concentrated urine and helping to maintain the body's water balance.
Therefore, the correct answer to the question is d. When ADH is secreted, water is reabsorbed from the urinary filtrate.