Role in Nutrient Absorption The lymphatic system also plays an important role in the absorption of nutrients. A system of lymph vessels runs alongside the intestines. The vessels pick up fats and fat-soluble vitamins from the digestive tract and transport these nutrients into the bloodstream.

Role in Immunity Hundreds of small bean-shaped enlargements—called lymph nodes—are scattered along lymph vessels throughout the body. Lymph nodes act as filters, trapping microorganisms, stray cancer cells, and debris as lymph flows through them. Fleets of white blood cells inside lymph nodes engulf or otherwise destroy this cellular “trash.” When large numbers of microorganisms are trapped in lymph nodes, the nodes become enlarged. The “swollen glands” that are symptoms of certain kinds of infections are actually swollen lymph nodes.

The thymus and spleen also play important roles in the immune functions of the lymphatic system. The thymus is located beneath the sternum. T lymphocytes mature in the thymus before they can function in the immune system. The functions of the spleen are similar to those of lymph nodes. However, instead of lymph, blood flows through the spleen, where it is cleansed of microorganisms and other debris. The spleen also removes old or damaged blood cells and stores platelets.

In Your Notebook Compare and contrast the functions of the circulatory system and the lymphatic system.

FIGURE 33–10 The Lymphatic System The lymphatic system is a network of vessels, nodes, and organs that recycles fluids from tissues and plays a role in nutrient absorption and immunity. Infer Why do you think your doctor feels your neck for swollen lymph nodes when you are sick?

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