Final answer:
The renin-angiotensin-aldosterone system is controlled by the kidneys and is vital for maintaining blood pressure and fluid balance by converting angiotensinogen to angiotensin II, which stimulates various responses to increase blood pressure.
Step-by-step explanation:
The renin-angiotensin-aldosterone system (RAAS) is essential for regulating blood pressure and fluid balance in the body. It begins when the kidneys release renin in response to low blood pressure or low sodium levels. Renin converts angiotensinogen, produced by the liver, into angiotensin I. This is then converted into angiotensin II by the angiotensin-converting enzyme (ACE) in the lungs. Angiotensin II has several effects: it constricts blood vessels to raise blood pressure, triggers the release of aldosterone from the adrenal cortex to increase sodium reabsorption in the kidneys, and prompts the release of anti-diuretic hormone (ADH) to enhance water retention.