The 레닌-안지오텐신-알도스테론 시스템 (RAAS) is a hormone system that regulates blood pressure and fluid balance in the body. It begins when the kidneys release 레닌, an enzyme that converts angiotensinogen, produced by the liver, into angiotensin I. This is then converted into angiotensin II, a powerful vasoconstrictor that increases blood pressure. Angiotensin II also stimulates the adrenal glands to release 알도스테론, a hormone that promotes sodium and water retention in the kidneys. This process helps to increase blood volume and pressure, ensuring that the body maintains adequate circulation and organ function.