Angiotensin I is a peptide hormone that plays a crucial role in the body's regulation of blood pressure and fluid balance. It is produced from angiotensinogen, a protein synthesized in the liver, through the action of the enzyme renin. Angiotensin I itself is relatively inactive but serves as a precursor to angiotensin II, a more potent hormone. Once formed, Angiotensin I is converted into Angiotensin II primarily by the enzyme angiotensin-converting enzyme (ACE) found in the lungs. Angiotensin II has significant effects, including constricting blood vessels and stimulating the release of aldosterone, which helps regulate sodium and water retention, ultimately influencing blood pressure.