PATHOLOGY

Detailed explanation-1: -One cell thick vessels are the blood vessels that join arteries and veins are the tiniest and most abundant blood vessels, called capillaries. They primarily serve the purpose of exchanging materials between the blood and tissue cells.

Detailed explanation-2: -The capillary walls are one cell thick. Capillaries allow molecules to pass through across the capillary walls. This exchange of materials is not possible across the walls of other types of blood vessels because the walls are too thick.

Detailed explanation-3: -The main function of capillaries is to transport digested food, oxygen, and other materials to all the cells of the body. Hence, their walls are thin, so that the substances can get in and out of them easily by diffusion.

Detailed explanation-4: -Endothelial cells form a single cell layer that lines all blood vessels and regulates exchanges between the bloodstream and the surrounding tissues. Signals from endothelial cells organize the growth and development of connective tissue cells that form the surrounding layers of the blood-vessel wall.