Immune System Organs
The human immune system includes various organs that help fight off infectious agents. The respiratory tract, the gastrointestinal tract, and the urogenital system all have mucosal epithelia surfaces. The epithelial cells line these surfaces and create a mucus layer to stop pathogens from adhering to the surface. These cells shed in the intestine, and they secrete substances like lysozyme and lactoferrin, which bind to and trap iron.
The thymus is an organ that primarily controls the maturation of T lymphocytes. It gradually disappears after eight months of age. The cortical microenvironment allows T cell progenitors to mature into mature T lymphocytes. The cells then undergo both positive and negative selection processes, enabling them to differentiate into non-self-reactive lymphocytes. T lymphocytes that express the TCR receptor molecules differentiate into mature T lymphocytes. Those that do not express these receptor molecules are excluded from the self-reactive lymphocyte population.
The bone marrow is another important part of the immune system. It contains myeloid progenitor cells, which develop into monocytes. Monocytes make up about two percent of blood and migrate into tissues where they develop into other types of immune cells called macrophages. These cells may survive for a long time and take on specific traits depending on their destination tissues. The lymphocytes in the blood are responsible for fighting germs and bacteria, and the bone marrow produces these cells.
In addition to the spleen, the lymphatic system includes the lymphatic system. This system consists of a network of lymphatic vessels that carry clear fluid called lymph throughout the body. The spleen, a large lymph node similar to a large femoral vein, is a lymph organ that functions like a filter for the blood. The spleen pulp synthesizes antibodies and removes bacteria and blood cells coated with antibodies. In addition, the nasopharyngeal tonsils are lymphoepithelial tissues and are the first line of defense for the immune system against ingested pathogens.