The Capillaries and Sinusoids

The capillaries are reduced to narrow endothelial tubes supported by a very delicate connective tissue investment. They allow escape of fluid from the blood into the tissue interstitium at the arterial end followed by the resorption of some fluid toward the venous end (see Fig.

Sinusoids constitute a special type of capillary found in certain organs, including the liver, spleen, and bone marrow. They are wider, less regular, and more commonly fenestrated than ordinary capillaries, and their endothelial cells are able to extract colloidal substances from the blood.