ISSA Nutritionist Practice Exam

Aldosterone is the hormone responsible for regulating sodium retention in the body, which leads to an increase in blood volume. It is produced by the adrenal glands and plays a crucial role in the renal system by acting on the kidneys to promote the reabsorption of sodium from urine back into the bloodstream. This reabsorption of sodium draws water along with it, thereby increasing the overall blood volume.

Cortisol, while having various functions including the regulation of blood sugar and the body's response to stress, does not primarily focus on sodium retention. Insulin, on the other hand, is primarily involved in glucose metabolism and does not directly influence sodium levels. Thyroxine is a thyroid hormone that regulates metabolism but does not have a significant role in sodium retention or blood volume modulation. Each of these hormones has distinct functions, but it is aldosterone that specifically facilitates sodium retention and, as a result, increases blood volume.