The renin-angiotensin system (RAS) is a hormone system that regulates blood pressure and fluid balance in the body. It is primarily responsible for maintaining homeostasis in the cardiovascular system. The system begins with the release of renin from the kidneys in response to low blood pressure, dehydration, or low sodium levels. Renin then converts angiotensinogen, a protein produced by the liver, into angiotensin I. Angiotensin I is further converted into angiotensin II by the enzyme angiotensin-converting enzyme (ACE), which is mainly found in the lungs. Angiotensin II is a potent vasoconstrictor that causes blood vessels to constrict, leading to an increase in blood pressure. It also stimulates the release of aldosterone from the adrenal glands, which promotes sodium and water reabsorption in the kidneys, further increasing blood volume and pressure. Dysregulation of the RAS can lead to hypertension, heart failure, and other cardiovascular diseases. Various drugs targeting different components of the RAS, such as ACE inhibitors and angiotensin II receptor blockers, are commonly prescribed to treat hypertension and heart failure.