THE CAPILLARIES AND SINUSOIDS
The capillaries are reduced to narrow endothelial tubes supported by a very delicate connective tissue investment. They are the exchange vessels from which fluid passes from the blood into the tissue interstitium at the arterial end of the loop and into which some fluid is resorbed toward the venous end (see Figure 7-29).
They permeate almost every tissue, although the density of the network varies considerably. The endothelium is described as complete, but minute pores are present in the (fenestrated) capillaries that are typical of some situations (e.g., in intestinal villi and in renal glomeruli).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 the ordinary capillary, and their endothelial cells are able to extract colloidal substances from the blood.
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