This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urinary System: Functional Anatomy and Urine Formation, Subject name: Physiology
Proteolytic enzyme Renin is present in? 
Select and explain. 
A. Lungs, B. Kidney, C. Liver, D. Stomach
B: Kidney
Answer: B: Kidney 
Explanation: ANSWER: (B) KidneyREF: Guyton 11th ed page 223, Gray's anatomy 39th ed page 1192Indirect repeat Physiology 2003Renin is a protein enzyme released by the kidneys when the arterial pressure falls too low. Renin itself is an enzyme, not a vasoactive substance. Renin acts enzymatically on another plasma protein, a globulin called renin substrate (or angiotensinogen), to release a 10-amino acid peptide, angiotensin I. Hence it is a proteolytic enzyme,