The lymphatic system consists of lymph, lymph vessels, lymph nodes, and three organs—the tonsils, thymus, and spleen. The lymphatic system has three main functions and is responsible for:
The fluid (lymph) circulating through the lymphatic system comes from the blood. It contains white blood cells (leukocytes) responsible for immunity as well as monocytes and lymphocytes. As certain constituents of blood plasma filtrate through tiny capillaries into the spaces between cells, it becomes interstitial fluid. Most interstitial fluid is absorbed from the interstitial (or intercellular) spaces by thin-walled vessels called lymph capillaries.
At this point of absorption, interstitial fluid becomes lymph and is passed through lymphatic tissue called lymph nodes. The nodes are found in clusters in such areas as the neck (cervic/al lymph nodes), under the arm (axill/ary lymph nodes), the pelvis (ili/ac lymph nodes), and the groin (inguin/al lymph nodes).
They act as filters against foreign materials. Eventually, lymph reaches large lymph vessels in the upper chest and reenters the bloodstream. (See Figure Interrelationship of the cardiovascular system with the lymphatic system. Blood flows from the heart to blood capillaries and back to the heart. Lymph capillaries collect tissue fluid, which is returned to the blood. The arrows indicate direction of flow of the blood and lymph..)
Similar to blood capillaries, (1) lymph capillaries are thin-walled tubes that carry lymph from the tissue spaces to larger (2) lymph vessels. Label these structures in Figure Lymphatic system.
Lymph/omais a malignant tumor of lymph nodes and lymph tissue.
Two main kinds of lymphomas are Hodgkin disease and non-Hodgkin lymphoma.
Similar to veins, lymph vessels contain valves that keep lymph flowing in one direction, toward the thorac/ic cavity.
The (3) thoracic duct and the (4) right lymphatic duct carry lymph into veins in the upper thoracic region. Label these two ducts in Figure Lymphatic system.
Small round structures called lymph nodes not only produce lymph/o/cytes, but also filter and purify lymph by removing such harmful substances as bacteria and cancerous cells. Lymph cells are known as lymph/o/cytes
The major lymph node sites are the (5) cervical nodes, (6) the axillary nodes, and (7) the inguinal nodes. Label the three major lymph node sites in Figure Lymphatic system.
Tonsil, Spleen, and Thymus
The (8) tonsil is a small mass of lymphoid tissue in the mucous membranes of the pharynx and base of the tongue. Tonsils consist of several masses and are the first line of defense from the external environment. They act as a filter to protect against bacteria and other harmful substances that may enter the body through the nose or mouth. Label the tonsil in Figure Lymphatic system.
The (9) spleen is located in the left upper quadrant (LUQ) of the abdomen and behind the stomach. It is the largest lymphatic organ in the body. Although the spleen is not essential to life, it plays an important role in the immune response by filtering blood in much the same way that lymph nodes filter lymph. Label the spleen in Figure Lymphatic system.
Path/o/gens of all types are filtered from the circulating blood by the macro/phages of the spleen. The spleen also removes and destroys old red blood cells (RBCs) from circulation. The spleen contains ven/ous sinuses that serve as a storage reservoir for blood. In emergencies, such as hem/o/rrhage, the spleen can release blood back into the general circulation.
The (10) thymus, also an endocrine gland, is a lymphatic organ. It is located near the middle of the chest (mediastinum) just beneath the sternum. Label the thymus in Figure Lymphatic system.
During fetal life and childhood, the thymus is quite large, but becomes smaller with age as it completes most of its essential work during childhood. The thymus plays an important role in the body’s ability to protect itself against disease (immunity), especially during the early years of growth.
The thymus secretes a hormone called thymosin, which stimulates the red bone marrow to produce T lymph/o/cytes, or T cells. T cells are important in the immune process. They originate in the bone marrow but migrate and mature in the thymus. Upon maturation, T cells enter the blood and circulate throughout the body, providing a mechanism of defense against disease because the cells attack and destroy foreign or abnormal cells.
Specific lymph/o/cytes that attack foreign agents such as viruses are known as T lympho/cytesor T cells.
Some T cells are called killer cells because they secrete immun/o/ logic/ally essential chemical compounds that destroy foreign cells. Killer Tlymph/o/cytes, also known as cyt/o/toxic Tlymph/o/cytes, are so named because they are capable of destroying specific cells. The killer cells also play a significant role in the body’s resistance to proliferation of cancer (CA) cells.
Cyt/o/tox/ic T lymph/o/cytesdefend against viral and fung/al infections. They are also responsible for transplant rejection reactions and for immun/o/logic/al surveillance against cancer.
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