Final answer:
Renin is made by the kidneys and is a crucial component of the renin-angiotensin-aldosterone system.
Step-by-step explanation:
Renin is made by the kidneys. Specifically, it is produced by specialized cells called juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity. Renin plays a crucial role in the renin-angiotensin-aldosterone system, which helps regulate blood pressure and fluid balance in the body.