Angiotensinogen is a plasma protein produced and released into the circulation by the liver cells. It is also known as renin substrate. It is the component of the renin-angiotensin system (RAS) , a hormone system which regulates blood pressure and fluid balance. So, the correct answer is 'Liver cells'.

Angiotensinogen is a protein that plays a crucial role in the renin-angiotensin-aldosterone system (RAAS), which helps regulate blood pressure and fluid balance in the body. The production and secretion of angiotensinogen occur in the liver cells.

Explanation:

Renin-angiotensin-aldosterone system (RAAS) is a complex physiological system that regulates blood pressure, fluid balance, and electrolyte homeostasis. The system comprises several components, including renin, angiotensinogen, angiotensin-converting enzyme (ACE), and angiotensin II (Ang II). The liver is the primary site of angiotensinogen production and secretion.

Here is a detailed explanation of the role of the liver in the production and secretion of angiotensinogen:

• Angiotensinogen is a glycoprotein synthesized in the liver cells, primarily in the hepatocytes.

• The liver cells secrete angiotensinogen into the bloodstream, where it circulates as an inactive precursor.

• When the blood pressure drops or there is a decrease in renal blood flow, the juxtaglomerular (JG) cells in the kidney release renin into the bloodstream.

• Renin acts on angiotensinogen to cleave off a 10-amino acid peptide called angiotensin I (Ang I).

• Ang I is then converted into angiotensin II (Ang II) by ACE, which is mainly found in the lungs.

• Ang II is a potent vasoconstrictor that increases blood pressure and stimulates the release of aldosterone from the adrenal cortex, which helps retain sodium and water in the body.

In summary, the liver plays a critical role in the production and secretion of angiotensinogen, which is the precursor to Ang II, a potent regulator of blood pressure and fluid balance.