    renin ( ), also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system (ras)âalso known as the renin-angiotensin-aldosterone axisâthat mediates extracellular volume (i.e., that of the blood plasma, lymph and interstitial fluid), and arterial vasoconstriction. thus, it regulates the body's mean arterial blood pressure. renin is often improperly referred to as a hormone although it has no peripheral receptors and rather has an enzymatic activity with which it hydrolyses angiotensinogen to angiotensin i. == biochemistry and physiology == ===structure=== the primary structure of renin precursor consists of 406 amino acids with a pre- and a pro-segment carrying 20 and 46 amino acids, respectively. mature renin contains 340 amino acids and has a mass of 37 kda. === secretion === the enzyme renin is secreted by the afferent arterioles of the kidney from specialized cells called granular cells of the juxtaglomerular apparatus in response to three stimuli: # a decrease in arterial blood pressure (that could be related to a decrease in blood volume) as detected by baroreceptors (pressure-sensitive cells). this is the most direct causal link between blood pressure and renin secretion (the other two methods operate via longer pathways). # a decrease in sodium chloride levels in the ultrafiltrate of the nephron. this flow is measured by the macula densa of the juxtaglomerular apparatus. # sympathetic nervous system activity, which also controls blood pressure, acting through the beta1 adrenergic receptors. human renin is secreted by at least 2 cellular pathways: a constitutive pathway for the secretion of prorenin and a regulated pathway for the secretion of mature renin. ===renin-angiotensin system === [[file:renin-angiotensin system in man shadow.
EC_3.4.23 Genes_mutated_in_mice Human_proteins Peptide_hormones Renal_physiology