Organs of the Lymphatic System
Lymphatic organs can be found all over the body. Lymphatic tissue is distinguished by its structure. While different organs differ in their details, all have a very loose scaffolding of fibres called reticular fibres, in which millions of lymphocytes are imbedded.
Most of the disease-fighting function of the adult mammal is carried out by thelymph nodes. These are bean shaped, and occur along the lymph ducts. They serve as tiny filters, in which the lymphocyrtes actively attack any foreign substances that pass through the tiny spaces between cells.
There are many clusters of lymph nodes. The three shown in the illustration are the cervical lymph nodes (in the neck), the axillary lymph nodes (in the armpit), and the inguinal lymph nodes (in the groin). These three sets are called palpable lymph nodes, because they can be felt from the outside. Swelling of these nodes indicates infection.
Three pairs of enlarged lymph nodes calledtonsils occur in the pharynx (chamber at the back of the nose and mouth). The pharyngeal tonsils, also called adenoids, are at the back of the sinuses, the palatine tonsils are in the palate that separates the nasal and oral cavities, and the lingual tonsils are at the base of the tongue. The tonsils seem to play an important role in the immune response in children.
Thethymus is a large gland that covers the top of the heart in children. Lymphocytes migrate to the thymus from the bone marrow, where they divide rapidly forming what are called T-lymphocytes (T for thymus). The T-lymphocytes then migrate to other lymphatic organs where they mature and divide further. After puberty, the thymus degenerates slowly. Its role appears to be more concerned with setting up the immune system, while the actual disease fighting properties are carried out elsewhere.
Thespleen is an interface between the blood and the lymphatic system. Knots of lymphatic tissue in the spleen add lymphocytes to the blood. The spleen also acts as a filter for the blood, and helps to destroy worn out red-blood cells. In the event of damage to the spleen, it can be removed and its functions will be carried out reasonably effectively by the liver, the bone marrow and the lymph nodes.