Final answer:
The tunica intima is composed of the basement membrane and endothelium in a capillary. This combination provides the necessary structure and permeability for the exchange of materials. The endothelium also helps to regulate blood flow and prevent clotting.
Step-by-step explanation:
The basement membrane and endothelium together make up the tunica intima of a capillary. This layer is essential for providing flexibility and strength to the vessel, ensuring that it maintains its structure while still allowing the exchange of materials between the bloodstream and surrounding tissues.
The endothelium is a specialized simple squamous epithelium that lines the entire vascular system, including capillaries, arteries, and veins. It plays a crucial role in regulating blood flow and pressure by releasing substances like endothelins and is also a critical barrier that prevents clot formation by separating the blood from the collagenous fibers in vessel walls. The basement membrane or basal lamina supports the endothelium, binding it to the connective tissue, providing strength, and facilitating the permeability needed for the exchange of molecules.
Capillaries, being the smallest blood vessels where the exchange of oxygen, carbon dioxide, and other substances takes place, have a wall that is typically comprised of the endothelial layer and the supporting basement membrane, without the additional layers found in larger vessels.