Final answer:
The presence of antidiuretic hormone (ADH) in the bloodstream stimulates the kidneys to reabsorb water, leading to increased blood volume and pressure, hence the renal tubules reabsorb sodium and water. This process concentrates urine and maintains body fluid balance.
Step-by-step explanation:
When the physiologic level of antidiuretic hormone (ADH) is present in the bloodstream, it leads to an increase in the reabsorption of water by the renal tubules. The ADH, also known as vasopressin, is produced by the hypothalamus and released from the posterior pituitary gland, targeting the kidneys. Its primary action is to regulate water balance by reducing urine volume and increasing water reabsorption. When ADH binds to receptors on the cells of the kidney tubules, it prompts the insertion of aquaporins, which are water channels that increase water permeability. As a result, water is reabsorbed back into the bloodstream, which leads to increased blood volume and pressure, and a concentrated urine output.
In this context, the correct answer to the student's question is B) the renal tubules are stimulated to reabsorb sodium and water. This action is critical for maintaining fluid balance and avoiding dehydration. It's also important to note that ADH can induce vasoconstriction at high levels, contributing to an increase in blood pressure.