Final answer:
Aldosterone is the hormone responsible for regulating blood pressure and volume by controlling Na⁺ and K⁺ concentrations in body fluids, working as part of the renin-angiotensin-aldosterone system to promote water retention and increase blood volume and pressure.
Step-by-step explanation:
The hormone that regulates blood pressure and volume by controlling the concentration of Na⁺ and K⁺ in body fluids is aldosterone. Aldosterone is a mineralocorticoid hormone produced by the adrenal cortex. Its release is stimulated by factors such as a decrease in blood concentrations of sodium ions, blood volume, or blood pressure, or by an increase in blood potassium levels. When aldosterone is released, it causes the kidneys to retain sodium (Na⁺), which in turn promotes water retention, thereby increasing blood volume and pressure. At the same time, the renal excretion of potassium (K⁺) is increased.
This process is a crucial part of the renin-angiotensin-aldosterone system, which is a complex mechanism that the body uses to regulate blood pressure and fluid balance. Specifically, aldosterone causes the reabsorption of sodium from urine, sweat, the pancreas, and saliva, which directly impacts blood volume and pressure.