This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidneys and Body Fluids, Subject name: Physiology
Renin in synthesized by: 
Select and explain. 
A. Granular cells, B. Intercalated cells, C. Interstitial cells, D. Macula densa cells
A: Granular cells
Answer: A: Granular cells 
Explanation: Ans. A. Granular cellsGranular cells (also known as juxtaglomerular cells) are located primarily in the wall of afferent arterioles and are the major site of renin synthesis and release, (the JG cells are modified smooth muscle cells of the tunica media of the afferent arteriole; since the muscle cell has been modified to assume secretory function, the JG cells are referred to as myo-epithelioid cells).