lymphatic system (redirected from Lymphatics)

lymphatic system (lĭmfăt`ĭk), network of vessels carrying lymph, or tissue-cleansing fluid, from the tissues into the veins of the circulatory system. The lymphatic system functions along with the circulatory system in absorbing nutrients from the small intestines. A large portion of digested fats are absorbed via the lymphatic capillaries. Like the blood circulatory system, the lymphatic system is composed of fine capillaries that lie adjacent to the blood vessels. These merge into larger tributaries known as trunks, and these in turn merge into two still larger vessels called ducts. The thoracic and right lymphatic ducts empty into the venous system in the region of the collarbones. Lymph, a colorless fluid whose composition is similar to that of blood except that it does not contain red blood cells or platelets, and contains considerably less protein, is continuously passing through the walls of the capillaries. It transports nutrients to the cells and collects waste products. Most of the lymph returns to the venous capillaries; however, a small amount (about 10%) enters the terminal lymphatic capillaries and is returned to the blood via the lymphatic system. The fluid that flows through the lymphatic system is functionally important because it contains substances having large molecules (such as proteins and bacteria) that cannot enter the small pores of the venous capillaries. Along the lymphatic network in certain areas of the body (neck, armpit, groin, abdomen, chest) are small reservoirs, the lymph nodes, which collect bacteria and other deleterious agents from the lymph which passes through them, and act as a barrier against the entrance of these substances into the bloodstream. In a disease state, therefore, the lymph nodes may become filled with harmful material to the degree where they can be seen or felt; therefore, enlarged lymph nodes are of diagnostic importance. Such enlargement of the lymph nodes can be a warning sign of various kinds of cancer, including breast cancer and Hodgkin's disease. In cases where a cancerous growth has developed, removal of lymph nodes may help to prevent its further spread. However, such a procedure also slows the flow of lymph and may thus render some of the body vulnerable to infection. See also lymphoma, non-Hodgkin's.

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lymphatic system

System of lymph nodes, vessels, and nodules and lymphoid tissue, including the thymus, spleen, tonsils, and bone marrow, through which lymph circulates and is filtered. Its primary function is to return proteins, waste products, and fluids to the blood; molecules too big to enter the capillaries pass through the more permeable walls of lymphatic vessels. Valves keep lymph flowing in one direction, more slowly than blood and at a lower pressure. The lymphatic system also has a role in the immune system. Nodes filter bacteria and foreign matter from lymph. Smaller nodules, which often produce lymphocytes, form in areas more exposed to such materials. They can merge and become permanent, as in the tonsils. Blockage of a lymph vessel may cause fluid to collect in the tissues, producing lymphedema (tissue swelling). Other lymphatic system disorders include lymphocytic leukemias and lymphoma. See also reticuloendothelial system.

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lymphatic system

an extensive network of capillary vessels that transports the interstitial fluid of the body as lymph to the venous blood circulation

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lymphatic system [lim′fad·ik ‚sis·təm]

(anatomy)

A system of vessels and nodes conveying lymph in the vertebrate body, beginning with capillaries in tissue spaces and eventually forming the thoracic ducts which empty into the subclavian veins.

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Lymphatic system

A system of vessels in the vertebrate body, beginning in a network of exceedingly thin-walled capillaries in almost all the organs and tissues except the brain and bones. This network is drained by larger channels, mostly coursing along the veins and eventually joining to form a large vessel, the thoracic duct, which runs beside the spinal column to enter the left subclavian vein at the base of the neck. The lymph fluid originates in the tissue spaces by filtration from the blood capillaries. While in the lymphatic capillaries it is clear and watery. However, at intervals along the larger lymphatic vessels, the lymph passes through spongelike lymph nodes, where it receives great numbers of cells, the lymphocytes, and becomes turbid.

The lymph nodes of mammals vary in number, size, form, and structure in different species. The amount of connective tissue of the lymph nodes, that is, the degree of development of the capsule and trabeculae, also varies in different mammals. Other lymphoid organs include the tonsils, thymus gland, and spleen, and in certain classes and groups of animals, structures which are confined to such groups, for instance, the bursa of Fabricius in the birds, a diverticulum from the lower end of the alimentary canal. See Spleen, Thymus gland, Tonsil

The functions of the lymphatics are to remove particulate materials such as molecular proteins and bacteria from the tissues; to transport fat from the intestine to the blood; to supply the blood with lymphocytes; to remove excess fluid; also to return to the bloodstream the protein which has escaped from the blood capillaries. Basically, the composition of lymph closely resembles that of the plasma; lymph contains all of the types of protein found in plasma, but in lower concentration. The composition of lymph varies to some extent from one part of the body to another. Thus, the lymph from the liver contains more protein than that from the skin.

The lymph nodes serve as filtering-out places for foreign particles, including microorganisms, because the lymph comes into intimate contact with the many phagocytic cells of the sinusoids. These macrophages are of both the fixed and free wandering types. In addition to the phagocytic function, lymphoid tissue produces antibodies, although the actual process of antibody formation is not well understood. See Cellular immunology, Phagocytosis