Lymphatic system

The lymphatic system helps maintain the fluid balance in the body tissues. Fluid can leak out of capillary beds into the interstitial spaces. The lymphatic system takes up this fluid and returns it to blood circulation. The lymphatic system consists of small capillaries, with blind endings, found in tissue spaces. These small vessels join up to form larger and larger vessels coalescing into a couple of rather larger channels which return fluid to the large blood vessels above the heart. The fluid they carry is similar to plasma and is called lymph.

Lymphocytes are major cells of the immune system and are found in lymph. Lymph nodes are nodules of lymphatic tissue interspersed along the pathway of the lymphatic system. Lymph moves slowly through the trabecular network of the nodes allowing them to collect bacteria and foreign bodies through phagocytosis. This capacity to filter the lymph of microorganisms makes the lymph nodes an important component of the immune system.

The pattern of flow of lymph from the tissues through various lymph nodes to the thoracic duct (the largest lymph channel) is well known. This is an important diagnostic tool, as lymph nodes can be observed for inflammation due to infection. The lymphatic system can also be a pathway for the spread of cancer cells. In a person with a tumor, the pattern of lymph flow can give clues to where secondary growths might be.

Most of the lymphatic vessels can not be seen during dissection except for maybe the thoracic duct. This large lymph channel collects the lymph from all vessels except those from the right side of head and right upper limb.

Other components of the lymphatic system include the palatine tonsils, the ligunal tonsils and the pharyngeal tonsils. The function of these structures was debatable for some time, but their importance seems to lie in their production of lymphocytes. The spleen and thymus are also sites of lymphocyte production although the thymus is active only in young people.

Category: Anatomy Notes