The Structure of a Capillary Wall Differs from That of a Vein

Question

The structure of a capillary wall differs from that of a vein or artery because
A) the capillary wall has only two tunics.
B) capillaries have more smooth muscle.
C) capillary walls have only endothelium and a basement membrane.
D) capillaries can constrict or dilate.
E) capillaries are impermeable to all substances.

Accepted Answer

Capillary walls consist only of endothelium and a thin basement membrane, making them uniquely suited for the exchange of gases and nutrients between blood and tissues. Unlike veins and arteries, they lack multiple tunics or layers and smooth muscle, and they do not constrict or dilate to the same extent. Capillaries are also selectively permeable, allowing certain substances to pass through.