What is the primary action of Renin in the body?

Renin is an enzyme produced by the kidneys that plays a crucial role in regulating blood pressure. Its primary action is to initiate the renin-angiotensin-aldosterone system (RAAS), which ultimately leads to an increase in blood pressure. When blood pressure drops or there is a decrease in blood flow to the kidneys, renin is released into the bloodstream.

Renin acts on angiotensinogen, a protein produced by the liver, converting it into angiotensin I. This peptide is then converted to angiotensin II by the angiotensin-converting enzyme (ACE) primarily in the lungs. Angiotensin II is a potent vasoconstrictor, meaning it narrows blood vessels, which raises blood pressure. Additionally, angiotensin II stimulates the adrenal glands to release aldosterone, a hormone that causes the kidneys to retain sodium and water, further contributing to increased blood volume and blood pressure.

In contrast, the other options do not accurately describe the primary role of renin in the body. Renin does not regulate blood sugar, increase oxygen levels, or directly lower blood pressure; its function is specifically tied to elevating blood pressure through the complex interplay of hormones and physiological responses.