Organs of the Immune System Key Health – Mr. Nguyen 1. Adenoid a. Adenoids are a patch of tissue that is high up in the throat, just behind the nose. They, along with the tonsils, are part of the lymphatic system. The lymphatic system clears away infection and keeps body fluids in balance. The adenoids and tonsils work by trapping germs coming in through the mouth and nose. Adenoids usually start to shrink after about age 5. By the teenage years, they are almost completely gone. By then, the body has other ways to fight germs. 2. Appendix a. The appendix is a small, pouch-like sac of tissue that is located in the first part of the colon (cecum) in the lower- right abdomen. Lymphatic tissue in the appendix aids in immune function. The official name of the appendix is vermiform appendix, which means "worm-like appendage." The appendix harbors bacteria. 3. Bone Marrow a. Bone marrow is a sponge-like tissue situated inside of the bones. Most defense cells are produced and then also multiply here. They then migrate from the bone marrow into the bloodstream and reach other organs and tissues, where the defense cells mature and specialize. At birth, many bones contain red bone marrow, which actively builds defense cells. During the course of life, more and more red bone marrow turns into fat tissue. Adults only have red bone marrow in a few bones, for example in the ribs, in the breast bone and in the pelvic bone. 4. Lymph Nodes a. The lymphatic system of lymph nodes and vessels is important for continually exchanging substances between the blood and the tissue in the body. Fluid constantly leaves the blood, and defense cells and proteins migrate into the surrounding tissue. Most of the fluid is later taken back into the blood vessels. The rest of it is removed by the drainage system of the lymph vessels, which forms a fine net of thin-walled vessels in the body. The lymph nodes filter and clean the lymph fluid (lymph) on its way to the larger lymph vessels. The lymph finally travels to a vein called the superior vena cava, where it enters the blood stream. Lymph nodes work like biological filter stations. They contain different defense cells, which trap pathogens and activate the production of specific antibodies in the blood. If lymph nodes become swollen, painful or hard, it can be a sign of an active defense reaction, for example in an infection or, in rare cases, in malignant changes of the body’s own cells. 5. Peyer’s Patch a. Peyer's patches are small masses of lymphatic tissue found throughout the ileum region of the small intestine. Also known as aggregated lymphoid nodules, they form an important part of the immune system by monitoring intestinal bacteria populations and preventing the growth of pathogenic bacteria in the intestines. 6. Skin a. The primary function of the skin is to act as a barrier. The skin provides protection from: mechanical impacts and pressure, variations in temperature, micro-organisms, radiation and chemicals. 7. Spleen a. The spleen is situated in the left upper abdomen, beneath the diaphragm. It has a variety of tasks in the defense system. In the unborn child, the spleen mainly produces blood and defense cells. After birth this organ is mainly responsible for removing blood cells and for specific defense functions. As part of the immune defense, the functions of the spleen include the following: It stores different defense cells that are released into the blood to get to the organs, if needed: macrophages, also called scavenger cells, can attack non-self-substances and pathogens directly. T lymphocytes inspect cell surfaces, help in controlling defense and can also directly destroy cells that have been recognized as non-self or as pathogens. B lymphocytes produce antibodies, if needed. It is responsible for removing red blood cells (erythrocytes). Blood platelets (thrombocytes), which are responsible for blood clotting together, are stored and removed in the spleen. So there is always a lot of blood flowing through the spleen tissue. At the same time this tissue is very soft. In heavy injuries, in an accident, for example, the spleen can therefore rupture easily. The spleen then needs to be operated on, because otherwise there is a danger of bleeding to death. If the bleeding cannot be stopped, and the spleen has to be removed, other defense organs take on most of its tasks. 8. Thymus a. The thymus, also called the thymus gland, is only fully developed in children. From adolescence onwards, it is slowly turned into fat tissue. The gland-like organ is situated behind the breast bone above the heart. Certain defense cells are differentiated in the thymus: the so-called T lymphocytes, or T cells for short, among other things, are responsible for coordinating the innate and the adaptive immune system. The T in T lymphocytes stands for thymus, the place where they mature. T cells move through the body and constantly watch the surfaces of all cells for changes. To be able to do this job, they learn in the thymus which structures on cell surfaces are self and which are non-self. When coming into contact with a non-self body, T cells turn into so-called T effector cells, which trigger and regulate different defense reactions. This type of cells includes T killer cells, which can destroy cells infected with a pathogen. T helper cells are another kind of effector cells, which support other immune cells in doing their work. In childhood, the thymus tissue also produces two hormones – thymosin and thymopoietin – which regulate the maturation of defense cells in the lymph nodes. 9. Tonsils a. Tonsils also belong to the defense system. Due to their special position at the throat and palate, their defense cells come into contact with pathogens especially soon, and can activate the immune system immediately. Their tissue contains mainly lymphocytes. In addition to the palatine tonsils on the right and left side, which are commonly just called tonsils, there are also the adenoids above the roof of the throat, the lingual tonsil at the base of the tongue, and more lymphatic tissue on the sides of the throat. This lymphatic tissue can take on the function of the adenoids, if these have been removed. .