Renin is an enzyme produced by the kidneys that plays a crucial role in regulating blood pressure and fluid balance in the body. It is released in response to low blood pressure, low sodium levels, or sympathetic nervous system stimulation. Renin initiates a cascade of reactions that ultimately leads to the production of angiotensin II, a powerful vasoconstrictor that increases blood pressure. The renin-angiotensin-aldosterone system (RAAS) is the hormonal system that includes renin and is vital for maintaining cardiovascular health. When renin is released, it converts angiotensinogen, a protein produced by the liver, into angiotensin I. This is then converted into angiotensin II by the enzyme angiotensin-converting enzyme (ACE), further influencing blood pressure and fluid retention.