The immune system consists of lymphoid organs, functioning in a very coordinated manner due to the mobile cells that make up them, migrating throughout the body. The immune system consists of central and peripheral organs. The central ones are: thymus (thymus gland) and bursa Fabricius (lymphoid formation of the intestine of birds), which cause cellular and humoral immunity. Peripheral organs include: blood and bone marrow, tonsils, spleen, lymph nodes, appendicular process, lymphoid elements located in internal organs.

Thymus is the lymphoepithelial organ. Finally formed by the fifth year of life. Achieves its maximum development to thirty years and then evolves to old age. Thymus is the center of immune surveillance. It generates T-lymphocytes, factors that control T-cells at a distance. The function of the tibial gland appears broader, since this organ reacts subtly to various physiological and pathological conditions. For example, during pregnancy, the thymus decreases 2-3 times. It is directly related to the formation of a "growth factor", is involved in the regulation and differentiation of somatic cells in the fetus. An important feature of the thymus is a high level of mitzes, independent of antigenic irritation.

Bursa Fabricius is a follicle-epithelial organ. It is found in birds. Regulates humoral immune responses. In humans, the function of the bursa is performed primarily by the appendix, bone marrow, lymphatic formations of the intestine.

Lymph nodes are located along the lymphatic vessels. They contain thymus-dependent and thymus independent centers. They are the place of formation of lymphocytes and the synthesis of antibodies. In the lymph nodes there is a retention of antigens, tumor and foreign cells, destruction of the red cells that have worked out their term.

The spleen is the largest lymphoid organ, the main source of circulating lymphocytes. As part of the reticulo-endothelial system, the spleen is destroyed and removed from the blood stream, which have lost functional activity, obsolete and damaged red blood cells, leukocytes, platelets, and also hemoglobin turns into bilirubin and hemosiderin. Since hemoglobin contains iron, the spleen is one of the richest iron reservoirs in the body. In addition, the spleen acts as a filter for bacteria, protozoa and foreign particles, produces antibodies, controls the cytological composition of the blood. People deprived of spleen, especially small children, are very sensitive to many bacterial infections. Finally, as an organ involved in the circulation, it serves as a reservoir of erythrocytes, which in a critical situation again enter the bloodstream.

Blood - conditionally refers to the "peripheral lymphoid organs." In the blood circulate various types of lymphocytes, monocytes, neurophiles and other cells of the internal environment. The total number of circulating lymphocytes is 10 to 10 degrees.

Palatine tonsils - represent a paired lymphoid organ, located in the threshold of the pharynx, on the border of the respiratory and digestive tracts. Performs a special role of the information center about foreign agents entering into the internal environment of the organism contained in food, water and air. Interstitial tissue of the palatine tonsils is a thymus-dependent information zone, and crypts with lymphoid nodules serve for the reproduction of B-lymphocytes. In tonsils, sIgA, IgM, IsG, and interferons are synthesized. All this determines the nonspecific anti-infective resistance of the body from birth.

The appendicular process - histomorphologically consists of a dome with a crown, follicles located under the dome, a thymus-dependent zone, and associated mucosa in the form of mushroom-shaped protrusions. The dome of the appendix performs the function of the central lymphoid organ, and in the follicles the B cells that are sensitized with intestinal bacteria multiply.