The lymphatic system
The lymphatic system is one of the body’s natural defences against infection and disease.
The lymphatic system is made up of lymphatic organs such as bone marrow, the tonsils, the thymus, the spleen and lymph nodes (sometimes called lymph glands).
The lymph nodes throughout the body are connected by a network of tiny lymphatic tubes (ducts). There are lymph nodes in many places in the body but they’re mainly found in the neck, armpit and groin. Their number varies from one part of the body to another, and there are very few in some parts. However, under your arm there may be 20-50 nodes.
Circulating the lymphatic vessels is a milky-looking fluid called lymph, which contains lymphocytes. Lymphocytes are white blood cells. They are an essential part of the body’s defence against infection and disease.
As it circulates, lymph passes through the lymph nodes, which filter out the bacteria that cause infection. So 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 that mature in the thymus gland (behind the breastbone) are called T-cells. Lymphocytes that mature in the bone marrow or lymphatic organs are called B-cells.