The renin-angiotensin system (RAS) is a hormone system that regulates blood pressure and fluid balance in the body. It begins when the kidneys release renin, an enzyme that converts angiotensinogen, produced by the liver, into angiotensin I. This inactive form is then converted into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE), primarily in the lungs. Angiotensin II has several effects, including constricting blood vessels, which increases blood pressure, and stimulating the release of aldosterone from the adrenal glands. Aldosterone promotes sodium and water retention in the kidneys, further increasing blood volume and pressure. This system plays a crucial role in maintaining cardiovascular health.