Angiotensin II is a potent that helps regulate blood pressure. Angiotensinogen, is an inactive hormone synthesized and released continuously from the . Its activation, which occurs within the , is initiated by the enzyme renin. Renin is released from the juxtaglomerular apparatus of the in response to either (1) blood pressure (as detected by decreased stretch of within granular cells, or by decreased NaCl detected by within macula densa cells); or (2) stimulation by the division. The sequential action of renin and angiotensin converting enzyme (ACE) causes the formation of angiotensin II (the active form of the hormone).