Lymphatic System: Parts, Function, and Immunity

What is the Lymphatic System?

Your lymphatic (lim-FA-tik) system not only helps the body defend itself against disease but also maintains homeostasis by keeping body fluids at a constant level. Body cells are constantly bathed in fluid. This tissue fluid is composed of water and dissolved substances that diffuse from the blood into the spaces between the cells that make up the surrounding tissues. This tissue fluid collects in open-ended lymph capillaries. Once the tissue fluid enters the lymph vessels, it is called lymph.

Lymph Nodes

A lymph node is a small mass of tissue that contains lymphocytes. It filters pathogens from the lymph. A lymphocyte is a type of white blood cell that defends the body against foreign substances.

Parts of the Lymphatic System

• Tonsils: Tonsils are large clusters of lymph tissue located at the back of the mouth cavity and the back of the throat. They form a protective ring around the openings of the nasal and oral cavities. Tonsils protect against bacteria and other pathogens that enter your nose and throat.

• Spleen: The spleen is an organ that stores certain types of lymphocytes. It also filters and destroys bacteria and worn-out red blood cells. The spleen does not filter lymph.
• Thymus Gland: Another important part of the lymphatic system is the thymus gland. It is located above the heart. The thymus gland stores immature lymphocytes until they mature and are released into the body’s defense system.

Antibody Immunity

Antibody immunity is a type of chemical warfare in your body that involves several types of cells.

When a pathogen invades the body, it is attacked by the cells of your innate immune system. If the infection is not controlled, then your body builds up acquired immunity. It produces antibodies to use against the antigen. A type of lymphocyte called a T cell becomes involved. A T cell is a lymphocyte that is produced in bone marrow and processed in the thymus gland. Two kinds of T cells play different roles in immunity:

B Cells

A B cell is a lymphocyte that becomes a plasma cell and makes antibodies when activated by a T cell. B cells are made in the bone marrow. Plasma cells release antibodies into the bloodstream and tissue spaces. Some activated B cells do not become plasma cells but remain in the bloodstream as memory B cells. Memory B cells are ready to respond if the same pathogen invades the body again.

Cytotoxic T Cells

Cellular immunity also involves T cells with antigens on their surfaces. The T cells involved in cellular immunity are cytotoxic, or killer, T cells. T cells, stored in the lymph nodes, spleen, and tonsils, transform into cytotoxic T cells. They are specific for a single antigen. However, unlike B cells, they do not form antibodies. Cytotoxic T cells produce identical clones. They travel to the infection site and release enzymes directly into the pathogens, which die.

Passive and Active Immunity

• Passive Acquired Immunity: Passive acquired immunity develops by acquiring antibodies that are generated in another host.
• Active Acquired Immunity: Active acquired immunity develops when your body produces antibodies in response to being exposed to antigens.

Types of Passive Immunity

• Natural Passive Immunity: Natural passive immunity develops when antibodies are transferred from a mother to her unborn baby through the placenta or to a newborn infant through the mother’s milk.
• Artificial Passive Immunity: Artificial passive immunity occurs when a human is injected with antibodies from a person or animal who is already immune.

Types of Active Immunity

• Natural Active Immunity: Active immunity can be gained naturally. When a person is exposed to particular antigens, the body produces antibodies that correspond to these antigens. When a person recovers from the infection, that person will usually be immune to the pathogen for the rest of his or her life.
• Artificial Active Immunity: Active immunity can be created artificially. This is done through vaccinations, usually a shot or injection, with a particular vaccine.