Lymphatics and Lymph Node Structure
The lymph system consists of a series of vessels, similar to blood vessels, and larger areas called nodes or nodules. These lymphatic vessels are spread throughout the body and carry 'lymph', an off-white fluid that is filled with lymphocytes, the cells that control the immune system and fight infections. The lymphatics enter nodes of varying size and importance and then leave to complete the circuit. The lymphocytes can leave the lymphatics to enter the blood stream and return to the lymphatics at any time.
Lymph nodes can be found throughout the body, including in the neck, armpits, abdomen, pelvis, and all the way down to the feet. In addition, there is other lymph tissue that plays a role in the immune system and this includes the tonsils and adenoids, thymus, bone marrow, spleen, and areas in the gastrointestinal tract.
There are several different types of cells present in any node and any one of these cells or a combination of them can be involved in lymphoma. Within a normal lymph node, one might find mature (functional) lymphocytes, immature lymphocytes, macrophages (cells that can ingest bacteria, viruses and damaged cells), and dendritic cells (specialised cells that help lymphocytes to function). Knowing which particular cells are involved is relevant to diagnosis.
Two of the most common cells within lymph nodes are called T and B cells. T lymphocytes can be thought of as the controllers of the immune system. They initiate the immune response, control how big or small it should be, and shut it down when it is not needed. In addition, they can neutralise several different types of foreign attackers. B lymphocytes make antibodies. It is these cells that you are training to respond to an attack when you get immunised against diseases, such as measles, mumps or hepatitis. T cells can attack on their own while B cells need T cells to help them.