Lymphoid tissue is found in many organs, including the lymph nodes, as well as in the lymphoid follicles in the pharynx such as the tonsils. Lymph nodes are found primarily in the armpits, groin, chest, neck, and abdomen. Lymphoid tissues contain lymphocytes (a type white blood cell), but they also contain other types of cells for structural and functional support, such as the dendritic cells, which play a key role in the immune system. The system also includes all the structures dedicated to the circulation and production of lymphocytes, including the spleen, thymus, and bone marrow.
• The lymphatic system is a circulatory system that drains fluid from the blood vessels.
• Lymph vessels are the site of fluid drainage and pump lymph fluid using smooth muscle and skeletal muscle action. The larger vessels contain valves to prevent backflow and pump towards the heart to return lymph fluid to the bloodstream by the subclavian veins.
• A lymph node is an organized collection of lymphoid tissue through which the lymph passes on its way to returning to the blood. Lymph nodes are located at intervals along with the lymphatic system.
• Lymphoid tissue contains lymphocytes and other specialized cells and tissues that have immune system functions.
lymph node: small oval bodies of the lymphatic system, distributed along the lymphatic vessels clustered in the armpits, groin, neck, chest, and abdomen. They filter through the lymph fluid.
lymph: a colorless, watery, bodily fluid carried by the lymphatic system, consisting mainly of white blood cells.
tonsils: masses of soft tissue present at the back of the throat formed of lymphatic tissue.
valves: the flaps present in the vessels to prevent the backflow of the fluid such as lymph and blood
lymphangion: the functional unit of a lymph vessel that lies between two semilunar valves, the lymph in it is moved by skeletal muscle contractions and arterial pulsations
subclavian vein: a large blood vessel that arises from the axillary vein in the neck
lymphocytes: white blood cells that are involved in the immune defence of the body
vena cava: the main vein in the body returning blood to the heart