The renin-angiotensin-aldosterone system (RAAS) is a hormone system that regulates blood pressure and fluid balance in the body. It begins when renin, an enzyme produced by the kidneys, is released in response to low blood pressure or low sodium levels. Renin converts angiotensinogen, a protein produced by the liver, into angiotensin I, which is then converted into angiotensin II by an enzyme in the lungs. Angiotensin II has several effects, including constricting blood vessels to increase 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.