Renin is an enzyme secreted by specialized cells in the kidneys when blood pressure drops too low, or when sodium levels in the body are low. Its primary role is to regulate blood pressure and maintain balance of sodium and potassium in the body
. Renin initiates the renin-angiotensin-aldosterone system (RAAS) by cleaving angiotensinogen, a protein produced by the liver, into angiotensin I. Angiotensin I is then converted into angiotensin II by angiotensin-converting enzyme (ACE) mainly in the lungs. Angiotensin II is a potent vasoconstrictor that narrows blood vessels, increasing vascular resistance and raising blood pressure. It also stimulates the adrenal glands to release aldosterone, which causes the kidneys to retain sodium and water, further increasing blood volume and blood pressure. Additionally, angiotensin II promotes the release of antidiuretic hormone (ADH) and triggers thirst to help restore blood volume
. Thus, renin itself does not directly raise blood pressure but acts as the key enzyme that starts a cascade leading to vasoconstriction, sodium and water retention, and ultimately increased blood pressure to restore kidney perfusion and electrolyte balance
. In summary, renin's main function is to respond to low blood pressure or low sodium by activating the RAAS, which raises blood pressure and helps maintain fluid and electrolyte homeostasis.
