Alung cell maintains homeostasis. of what is this an example? a: intercellular communication b: intracellular communication c: ion channel-linked receptor d: enzyme-linked receptor

The right answer is A: intercellular communication.

An example of intercellular communication is the one between the kidney, liver and lungs to preserve water-soluble homeostasis.

Angiotensinogen, an inactive protein produced by the liver, circulates in the blood. It is the precursor of the active peptides angiotensin I and II, and the only substrate of renin.

In the event of a drop in the pressure in the renal artery, renin (an enzyme sometimes considered as a hormone) is secreted in the kidney by differentiated myoepithelial cells of the arteriole afferent of the juxtaglomerular apparatus. There are also other stimuli promoting renin secretion: decreased natremia in the distal convoluted tubule, ß-agonists, hyperkalemia, PGI2 and stimulation of juxta-glomerular cells by the sympathetic nervous system)

The angiotensinogen is cleaved by the renin and forms a decapeptide called "angiotensin I", inactive.

Angiotensin I will then be converted primarily to angiotensin II by a carboxypeptidase, the angiotensin converting enzyme. This enzyme, secreted by the liver, acts at the pulmonary level.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.