Final answer:
Renin initiates the RAAS, leading to the production of angiotensin II, which increases blood pressure by vasoconstriction and stimulates aldosterone and ADH release for water and sodium retention.
Step-by-step explanation:
Role of Renin in Blood Pressure Regulation
Renin plays a critical role in the regulation of blood pressure by initiating the renin-angiotensin-aldosterone system (RAAS). When blood pressure is low, renin is secreted by the granular cells of the juxtaglomerular apparatus located in the kidneys' afferent and efferent arterioles. Renin then acts on a plasma protein called angiotensinogen, which is produced in the liver, converting it into angiotensin I. Angiotensin I, in turn, is transformed into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE), predominantly in the lungs.
Angiotensin II serves to increase blood pressure by causing vasoconstriction, or the narrowing of blood vessels. Moreover, it stimulates the adrenal cortex to release the mineralocorticoid aldosterone, leading to sodium and water reabsorption by the kidneys, which also contributes to an increase in blood pressure. Additionally, angiotensin II promotes the release of anti-diuretic hormone (ADH), which encourages water retention in the kidneys, further helping to elevate blood pressure. A key method for controlling high blood pressure medically involves the use of ACE inhibitors, which prevent the conversion of angiotensin I to angiotensin II, thereby reducing the effects of aldosterone and ADH on raising blood pressure.