Final answer:
The renin-angiotensin-aldosterone axis regulates blood pressure and fluid balance through a chain reaction initiated by the release of renin, which converts angiotensinogen into angiotensin II, leading to vasoconstriction and the release of aldosterone, which increases blood pressure and volume.
Step-by-step explanation:
The renin-angiotensin-aldosterone axis is a critical regulatory system of the body that controls blood pressure and fluid balance. When blood pressure drops or there is a decrease in sodium chloride concentration, specialized cells in the kidneys called juxtaglomerular (JG) cells release the enzyme renin. Renin catalyzes the transformation of the liver-produced plasma protein angiotensinogen into angiotensin I, which is then converted to angiotensin II by angiotensin-converting enzyme (ACE) in the lungs.
Angiotensin II has several functions: it constricts blood vessels to increase blood pressure, stimulates the adrenal cortex to release aldosterone, and triggers the hypothalamus to release anti-diuretic hormone (ADH), leading to water retention in the kidneys. Aldosterone causes the renal tubules to reabsorb more sodium, which increases blood volume and pressure. In medical contexts, drugs known as ACE inhibitors can be used to manage high blood pressure by blocking this system.