Renin is best described as which of the following?

• A. A hormone secreted by the kidney
• B. A digestive enzyme
• C. A neurotransmitter
• D. A vitamin

Answer: (A)

Renin is produced by the kidney and released into the bloodstream to start a regulatory cascade that controls blood pressure and fluid balance. Its function is enzymatic: it cleaves angiotensinogen, a protein produced by the liver, to form angiotensin I, which is then processed further to raise blood pressure. Among the given descriptions, the label that identifies the kidney as the source is the best match, since renin is indeed secreted by the kidney. The other choices don’t fit its role or origin (it’s not a digestive enzyme, a neurotransmitter, or a vitamin). In more precise terms, renin is an enzyme, not a hormone, but the correct answer here reflects its renal origin.