Renin–angiotensin system

Plasma renin then carries out the conversion of angiotensinogen, released by the liver, to a decapeptide called angiotensin I, which has no biological function on its own.

Then, it is rapidly degraded into a heptapeptide called angiotensin III by angiotensinases which are present in red blood cells and vascular beds in many tissues.

[9][11][12] Outside the kidneys, renin is predominantly picked up from the circulation but may be secreted locally in some tissues; its precursor prorenin is highly expressed in tissues and more than half of circulating prorenin is of extrarenal origin, but its physiological role besides serving as precursor to renin is still unclear.

[13] Outside the liver, angiotensinogen is picked up from the circulation or expressed locally in some tissues; with renin they form angiotensin I, and locally expressed angiotensin-converting enzyme, chymase or other enzymes can transform it into angiotensin II.

[17] Other places of expression include the reproductive system, the skin and digestive organs.

Renin levels are high in the fetus, while angiotensin II levels are significantly lower; this is due to the limited pulmonary blood flow, preventing ACE (found predominantly in the pulmonary circulation) from having its maximum effect.