MEDICAL PHYSIOLOGY

Detailed explanation-1: -Most capillaries are only about 8 to 10 micrometers in diameter (a micrometer is 0.001 mm). They’re so tiny that red blood cells have to pass through in a single file line.

Detailed explanation-2: -It is important for capillaries to be narrow blood vessels that force red blood cells to move in single file because it allows for these cells to drop off oxygen molecules and pick up carbon dioxide molecules. The wall of the capillaries is thin enough to allow gas exchange to occur.

Detailed explanation-3: -Blood capillaries are made up only of endothelial cells. It is a single layer in thickness.