The Human Body

Lymphatic System

Lymphatic System, common name for the circulatory vessels or ducts in which the fluid bathing the tissue cells of vertebrates is collected and carried to join the bloodstream proper (see Lymph). The lymphatic system is of primary importance in transporting digested fat from the intestine to the bloodstream; in removing and destroying toxic substances; and in resisting the spread of disease throughout the body.

The portions of the lymphatic system that collect the tissue fluids are known as lymphatic capillaries and are similar in structure to ordinary capillaries. The lymphatic capillaries that pick up digested fat in the villi of the intestine are known as lacteals. The lymphatic capillaries are more permeable than ordinary capillaries and allow passage of larger particles than would ordinarily pass through capillary walls; large-molecule proteins, produced as a result of tissue breakdown, pass into the lymphatics for transport away from the tissues.

Among the abnormal conditions affecting the lymphatic system are inflammation of the lymphatics or of the lymph nodes, seen in infections; tuberculosis of the lymph nodes; malignancies in the lymphatic system (see Cancer; Hodgkin's Disease); and elephantiasis.


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