PATHOLOGY

Detailed explanation-1: -Capillaries are thin-walled vessels composed of a single endothelial layer. Because of the thin walls of the capillary, the exchange of nutrients and metabolites occurs primarily via diffusion.

Detailed explanation-2: -The endothelial tunic is continuous with the endocardium of the heart. In capillaries, this single layer of cells is the location of diffusion of oxygen and carbon dioxide between the endothelial cells and red blood cells, as well as the exchange site via endocytosis and exocytosis.

Detailed explanation-3: -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.