What is the precursor protein for the production of angiotensin II?

The correct answer is angiotensinogen, which serves as the precursor protein for angiotensin II. Angiotensinogen is synthesized and released by the liver and is a large plasma protein that serves as the starting point in the renin-angiotensin system. When renin, an enzyme secreted by the kidneys in response to low blood pressure or low sodium levels, cleaves angiotensinogen, it produces angiotensin I. This inactive form is then converted to angiotensin II primarily by the action of angiotensin-converting enzyme (ACE) found in the lungs.

Angiotensin II is a potent vasoconstrictor that plays a critical role in regulating blood pressure and fluid balance in the body. Therefore, identifying angiotensinogen as the precursor highlights its fundamental importance in the cascade of reactions leading to the formation of angiotensin II.

Other options are related but not precursors to angiotensin II. Aldosterone is a hormone formed in the adrenal glands that regulates sodium and potassium levels and is influenced by angiotensin II. Renin is an enzyme that initiates the conversion process but is not a protein precursor itself. ADH, or antidiuretic hormone, regulates water balance in the