Angiotensin is part of an elaborate group of linked hormones, enzymes, proteins and reactions called the renin-angiotensin-aldosterone system that helps regulate blood pressure.
To start the system or cycle, when blood pressure falls, your kidneys release the enzyme renin into your bloodstream.
Renin splits angiotensinogen, a protein made in your liver and releases the pieces.
One piece is the hormone angiotensin I.
Angiotensin I, which is inactive (doesn’t cause any effects), flows through your bloodstream and is split by angiotensin-converting enzyme (ACE) in your lungs and kidneys.
One of those pieces is angiotensin II, an active hormone.
Angiotensin II causes the muscular walls of small arteries (arterioles) to constrict (narrow), increasing blood pressure.
Angiotensin II also triggers your adrenal glands to release aldosterone and your pituitary gland to release antidiuretic hormone (ADH, or vasopressin).
Together, aldosterone and ADH cause your kidneys to retain sodium.
