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Biology - The Lymphatic System

The lymph system is another system of vessels with liquid in them. The vessels are called the lymphatics and the fluid is called the lymph. Every so often, along the course of every lymph vessel there is a little thing called a lymph node. A lymph node is made up mostly of some cells called lymph cells. Another word for lymph cells is lymphocytes. Lymphocytes are found not only in the lymph nodes but they circulate in the blood as well. Lymph nodes collect and return interstitial fluid to the blood. They are composed of lymphocytes and are therefore important in protecting the body against infection. 

The spleen is like one giant lymph node full of lymphocytes. The spleen also destroys old red blood cells. The thymus is important in the development of lymphocytes. There are two main types of lymphocytes. T lymphocytes arise in the bone marrow and mature in the thymus. They are responsible for cellular immunity. B lymphocytes are made in the bone marrow also. They are responsible for humoral immunity. In order to have a fully functioning immune system, you need to have both B and T lymphocytes in your lymphatics and your blood. Since lymphocytes do circulate in the blood, they are regarded as blood cells. When foreign substances known as antigens enter the blood, they cause B lymphocytes to make protein antibodies. These antibodies bind to the foreign materials and make them easier to destroy. There are many different types of T lymphocytes. T lymphocytes destroy antigens and often work with B lymphocytes.