E. L. Steele Laboratory, Department of Radiation Oncology, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts. Show Address correspondence to: Timothy P. Padera, PhD, Massachusetts General Hospital, Radiation Oncology-Cox 7, 100 Blossom Street, Boston, MA 02114. E-mail:ude.dravrah.hgm.eleets@aredapt Funding support: The authors are supported by NIH R00CA137167, NIH DP2OD008780, NIH R21AI097745 and NCI Federal Share/Proton Beam Income (TPP), Charles King Trust Fellowship and NIH K99HL111343 (SL). Our immune system is made up of both individual cells and proteins as well as entire organs and organ systems. The organs of the immune system include skin and mucous membranes, and the organs of the lymphatic system too. Organs that function as barriersYour skin and mucous membranes are the first line of defense against germs entering from outside the body. They act as a physical barrier with support from the following:
In addition, the reflexes that cause us to cough and sneeze help to free our airways of germs. The parts of the immune system Lymphoid organsThe lymphatic system is composed of:
Bone marrowBone marrow is a sponge-like tissue found inside the bones. That is where most immune system cells are produced and then also multiply. These cells move to other organs and tissues through the blood. At birth, many bones contain red bone marrow, which actively creates immune system cells. Over the course of our life, more and more red bone marrow turns into fatty tissue. In adulthood, only a few of our bones still contain red bone marrow, including the ribs, breastbone and the pelvis. ThymusThe thymus is located behind the breastbone above the heart. This gland-like organ reaches full maturity only in children, and is then slowly transformed to fatty tissue. Special types of immune system cells called thymus cell lymphocytes (T cells) mature in the thymus. Among other tasks, these cells coordinate the processes of the innate and adaptive immune systems. T cells move through the body and constantly monitor the surfaces of all cells for changes. Lymph nodesLymph nodes are small bean-shaped tissues found along the lymphatic vessels. The lymph nodes act as filters. Various immune system cells trap germs in the lymph nodes and activate the creation of special antibodies in the blood. Swollen or painful lymph nodes are a sign that the immune system is active, for example to fight an infection. SpleenThe spleen is located in the left upper abdomen, beneath the diaphragm, and is responsible for different kinds of jobs:
There is always a lot of blood flowing through the spleen tissue. At the same time this tissue is very soft. In the event of severe injury, for example in an accident, the spleen may rupture easily. Surgery is then usually necessary because otherwise there is a danger of bleeding to death. If the spleen needs to be removed completely, other immune system organs can carry out its roles. TonsilsThe tonsils are also part of the immune system. Because of their location at the throat and palate, they can stop germs entering the body through the mouth or the nose. The tonsils also contain a lot of white blood cells, which are responsible for killing germs. There are different types of tonsils: palatine tonsils, adenoids and the lingual tonsil. All of these tonsillar structures together are sometimes called Waldeyer's ring since they form a ring around the opening to the throat from the mouth and nose. There is also lymphatic tissue on the side of the throat, which can perform the functions of the palatine tonsils if they are removed. Mucous membranesThe bowel plays a central role in defending the body against germs: More than half of all the body's cells that produce antibodies are found in the bowel wall, especially in the last part of the small bowel and in the appendix. These cells detect foreign substances, and then mark and destroy them. They also save information about the substances in order to be able to react more quickly the next time. The large bowel also contains harmless bacteria called gastrointestinal or gut flora. Healthy gut flora make it difficult for germs to spread and enter the body. Mucous membranes support the immune system in other parts of the body, too, such as the respiratory and urinary tracts, and the lining of the vagina. The immune system cells are directly beneath the mucous membranes, where they prevent bacteria and viruses from attaching. Sources
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