The capillaries have walls which are one-cell thick. Give reason.

• The one-cell thickness of the walls of the capillaries makes them very thin and hence permeable.
• The cells take up useful substances from the tissue fluid and give out the waste substance in the tissue fluid.
• The substances from capillaries can easily diffuse in or diffuse out between the capillaries and the tissues fluid easily due the permeability of capillaries.