4.11: Lymphatics and the Spleen

The structure and valves of lymph vessels are very much like those of veins. Lymph flowing through lymph vessels passes through lymph nodes, which are spongy structures ranging up to the size of a large bean (Figure 4.2). Lymph nodes contain defense cells that neutralize or remove harmful chemicals and microorganisms. By acting like purifying filters, lymph nodes reduce the risk of spreading dangerous materials from a site of injury or infection in one area of the body to another region.

Much lymph passes through the spleen, which is toward the back of the abdominal cavity near the lowest rib on the left side of the body. The spleen serves as a very large lymph organ, stores blood, and removes old and damaged red blood cells from the circulation.

Some defense cells in the lymph nodes and spleen are called macrophages because they ingest substances. Others are called lymphocytes. Macrophages and lymphocytes are parts of the immune system.

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