The Lymphatic System

What is the function of the lymphatic system?

As blood passes through capillaries, some blood cells and components of plasma move through capillary walls and into the fluid between cells, carrying nutrients, dissolved oxygen, and salts. Each day about 3 liters of fluid, and the small particles it contains, leaves the blood. Most of this fluid, known as lymph, is reabsorbed into capillaries, but not all of it. The rest goes into the lymphatic system. The lymphatic system is a network of vessels, nodes, and organs that collects the lymph that leaves capillaries, “screens” it for microorganisms, and returns it to the circulatory system. The lymphatic system, shown in Figure 33–10, is also involved in the absorption of nutrients and in immunity.

Role in Circulation Lymph collects in a system of lymphatic capillaries that slowly conducts it into larger and larger lymph vessels. The lymphatic system doesn't have a pump to move lymph along. Instead, lymph vessels have valves, similar to the valves in large veins, that prevent lymph from flowing backward. Pressure on lymph vessels from surrounding skeletal muscles helps move lymph through the system into larger and larger ducts. These ducts return lymph to the blood through openings in the subclavian veins just below the shoulders. When injury or disease blocks lymphatic vessels, lymph can accumulate in tissues, causing swelling called edema.