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1-7. LYMPHATIC SYSTEM
The lymphatic system consists of lymph, lymph vessels, and lymph nodes. The spleen belongs, in part, to the lymphatic system. Unlike the cardiovascular system, the lymphatic system has no pump to move the fluid that collects, but muscle contractions and breathing movements aid in the movement of lymph through its channels and its return to the blood stream.
a. Lymph and Tissue Fluid. Lymph, fluid found in the lymph vessels, is clear and watery and is similar to tissue fluid, which is the colorless fluid that fills the spaces between tissues, between the cells of organs, and between cells and connective tissues. Tissue fluid serves as the "middleman" for the exchange between blood and body cells. Formed from plasma, it seeps out of capillary walls. The lymphatic system collects tissue fluid, and as lymph, the collected fluid is started on its way for return to the circulating blood.
b. Lymph Vessels. Starting as small blind ducts within the tissues, the lymphatic vessels enlarge to form lymphatic capillaries. These capillaries unite to form larger lymphatic vessels, which resemble veins in structure and arrangement. Valves in lymph vessels prevent backflow. Superficial lymph vessels collect lymph from the skin and subcutaneous tissue; deep vessels collect lymph from all other parts of the body. The two largest collecting vessels are the thoracic duct and the right lymphatic duct. The thoracic duct
receives lymph from all parts of the body except the upper right side. The lymph from the thoracic duct drains into the left subclavian vein, at the root of the neck on the left side. The right lymphatic duct drains into a corresponding vein on the right side.
c. Lymph Nodes. Occurring in groups up to a dozen or more, lymph nodes lie along the course of lymph vessels. Although variable in size, they are usually small oval bodies that are composed of lymphoid tissue. Lymph nodes act as filters for removal of infective organisms from the lymph stream. Important groups of these nodes are located in the axilla, the cervical region, the sub maxillary region, the inguinal (groin) region, and the mesenteric (abdominal) region.
d. Infection and the Lymphatic System. Lymph vessels and lymph nodes often become inflamed as the result of infection. An infection in the hand may cause inflammation of the lymph vessels as high as the axilla (armpit). A sore throat may cause inflammation and swelling of lymph nodes in the neck (submandibular nodes below the jaw and cervical nodes posteriorly).
e. Spleen. The largest collection of lymphoid tissue in the body, the spleen is located high in the abdominal cavity on the left side, below the diaphragm and behind the stomach. It is somewhat long and ovoid (egg- shaped). Although it can be removed (splenectomy) without noticeable harmful effects, the spleen has useful functions, such as serving as a reservoir for blood and red blood cells.
