The lymphatic system

It is a complex system made up of lymphatic organs, such as bone marrow, tonsils, the spleen, and lymph nodes (also called lymph glands). They are connected by a network of tiny lymphatic vessels. Lymph nodes are mainly found in the neck, armpit and groin. The number of nodes varies from one part of the body to another. In some parts there are very few. However, under your arm there may be between 20 and 50 nodes (see the diagram below).  

The lymphatic system
View a large copy of the diagram of the lymphatic system|

Circulating through the lymphatic vessels is milky-looking fluid called lymph. Lymph contains lymphocytes, which are white blood cells. They are an essential part of the body’s defence against infection and disease. For example, if you have a sore throat, you may notice that the lymph nodes in your neck get larger. This is a sign that your body is fighting the infection.

There are two main types| of lymphocyte: T-cells and B-cells. All lymphocytes develop in the bone marrow from immature cells called stem cells. Lymphocytes which mature in the thymus gland (behind the breast bone) are called T-cells. Other lymphocytes mature in the bone marrow or lymphatic organs and are called B-cells.