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Lymphocytes and Lymphatic System

Immunity is the result of the action of two types lymphocytes, the B lymphocytes and the T lymphocytes.

The B and T cells are produced in the bone marrow.  The T cells mature in the thymus gland while the B cells mature in the bone marrow.  Millions of these matured B and T cells move through the circulatory and lymphatic systems.

B and T cells have different functions.  B cells produce antibodies that are secreted into the blood and lymph.  Unlike B cells, the T cells do not produce antibodies.  Instead the T cells just attack the cells that have antigens that they recognize.  It has been estimated that during our lifetime, we will encounter a million different antigens, and our bodies need the same amount of lymphocytes to defend against them.  There will always be a different type of lymphocyte for each possible antigen.  None of these lymphocytes are supposed to attack the body’s own cells.  It very rarely may be possible that a lymphocyte will respond to the body’s own proteins.                                                                                          

Rather than a circulatory system, the lymphatic system is a one way system, and contains lymph veins and capillaries only.  The lymphatic system begins with lymph veins and capillaries that lie near the blood capillaries.  They take up any excess tissue fluid.  Once the tissue fluid has entered the lymph capillaries it is called lymph.

Lymph in humans moves through the lymph capillaries and vessels as a result of pressure applied by muscle contractions near the vessels.  Valves prevent the lymph from flowing backwards. Lymph moves through smaller vessels that join to form larger vessels, which then goes into two major lymph ducts that empty into large blood circulatory veins of the shoulders near the heart.

The lymphatic system has several other functions.  Lymph vessels known as lacteals are present within the intestinal villi. The products of fat digestion enter the lacteals and are carried in lymph vessels to enter the circulatory system.  Lymph nodes are small round structures made out of lymphnoid tissue.  Lymphocytes are packed into the spaces of a lymph node, which filters and traps bacteria and other debris, help keeping the blood clean.  When there is a small infection, such as a sore throat, lymph nodes in that region may swell and become painful.