Question

Blood capillaries are made up of

• A. Endothelium and thin coat of connective tissue
• B. Endothelium and thin coat of muscle fibres
• C. Endothelium and thin coat of connective tissue and muscle fibres
• D. Only endothelium

Answer 1

Answer: (D)

Only endothelium

Capillaries allow for exchanges between the blood and body cells, or between the blood and air in the lung tissues. The capillaries connect the arterioles and venules. Capillaries are microscopic structures. The most important structural feature of capillaries is their extreme thinness only one layer of flat, endothelial cells composes the capillary membrane. Instead of three layers or coats in arteries and veins, the capillary wall is composed of only one layer, the tunica interna. Substances such as glucose, oxygen, and wastes can quickly pass through it on their way to or from the cells. Smooth muscle cells, that are called precapillary sphincters guard the entrance to the capillary and determine into which capillary blood will flow.