The Renin-Angiotensin-Aldosterone System (RAAS) is a hormone system that regulates blood pressure and fluid balance in the body. It starts 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 in the lungs, which constricts blood vessels and stimulates the release of aldosterone from the adrenal glands. Aldosterone promotes sodium and water retention in the kidneys, increasing blood volume and pressure. RAAS plays a crucial role in maintaining cardiovascular health, but overactivity can lead to conditions like hypertension and heart failure. Medications that target RAAS are often used to treat these issues.