What is the primary function of the renin-angiotensin-aldosterone system (RAAS)?

• A. Regulates body temperature through metabolic changes
• B. Regulates blood pressure and fluid balance
• C. Increases metabolic rate during physical activity
• D. Promotes muscle growth and recovery

Answer: (B)

The primary function of the renin-angiotensin-aldosterone system (RAAS) is to regulate blood pressure and fluid balance. This system is crucial for maintaining homeostasis within the body, particularly in response to changes in blood volume and blood pressure. When blood pressure drops or there is a decrease in blood flow to the kidneys, renin is released from the juxtaglomerular cells. Renin then converts angiotensinogen, produced by the liver, into angiotensin I, which is further converted to angiotensin II by the action of the enzyme ACE (angiotensin-converting enzyme).

Angiotensin II has several key effects: it constricts blood vessels, leading to increased blood pressure, and it stimulates the adrenal cortex to release aldosterone. Aldosterone promotes sodium and water reabsorption in the kidneys, which further contributes to raising blood volume and, consequently, blood pressure. Thus, the RAAS plays an essential role in regulating blood pressure and fluid homeostasis, making option B the correct choice.

The other options do not accurately reflect the functions of the RAAS. Regulating body temperature, increasing metabolic rate, and promoting muscle growth and recovery are not linked to this hormonal system; they involve other