Human Anatomy Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovskyi 2008

Special Part
Hematopoietic Organs and the Immune System - General Information

One of the primary Functions of the Hematopoietic Organs is The ability to produce Blood Cells, i.e., hematopoiesis (from the Greek haema - blood, poetin - to make). Embryonic Stem Cells formed in the Bone Marrow give rise to all Cells of the blood and The Immune System.

The immune system is an anatomical and functional System of the body of higher animals and humans that performs protective functions to maintain internal antigenic Homeostasis. The immune system monitors abnormal Cell Division within the body, preventing the potential development of Cancer (malignant tumors) at early stages. With age or when affected by disease, especially AIDS, the Immune Response is suppressed, increasing the risk of developing malignancies.

The tissue in which blood cells and their immediate precursors are formed is called hematopoietic tissue. There are two types of hematopoietic Tissues: myeloid and lymphoid. Myeloid tissue gets its name from the Greek myelos - marrow; erythrocytes, granular leukocytes, and platelets are formed in it. Lymphoid tissue* is rich in lymphocytes and their precursors; it is located in the Thymus, Lymph Nodes, and Spleen. In 1969, B. Anderson and H. Wigzell divided all lymphocytes into T-lymphocytes and B-lymphocytes.

The following main classes of lymphocytes are distinguished:

1. T-lymphocytes**, which are the primary effectors of cell-mediated Immunity. The BIOCHEMICAL BASIS OF The Cell-mediated immune response is the cytotoxic effect against foreign cells, mediated by lysosomal Hydrolases of T-lymphocytes. In addition, T-lymphocytes participate in a complex network of regulatory reactions that modulate the functional activity of B-lymphocytes.

2. B-lymphocytes, which are the effectors of humoral immunity and the precursors of antibody-producing plasma cells—the primary producers of Antibodies (IMMUNOGLOBULINS).

* Lymphoid tissue (Lat. lympha - clear Water + Greek eidos - appearance; syn. lymphatic tissue) is a morphofunctional complex of lymphocytes and macrophages located within a cellular-Fibrous Connective Tissue framework, constituting the functional parenchyma of Lymphoid organs.

** Several types (subpopulations) of T-lymphocytes are distinguished:

a) T-killer cells (Tk), or T-effector cells (Te) — "killer" lymphocytes that mediate cell-mediated immune responses; they target and destroy target cells (J. Roder et al., 1978).

b) T-helper cells (Th) — cells that play an auxiliary role in humoral and cell-mediated immune responses (G. Chell, 1978).

c) T-suppressor cells (Ts) — lymphocytes that suppress or inhibit The Development of humoral and cell-mediated immune responses, promoting the establishment of immunological tolerance (R. Stout et al., 1983; D. Parkis, 1984).

3. Null lymphocytes — cells that differ from T- and B-lymphocytes; they include cytotoxic cells and a certain population of killer lymphocytes, the so-called "natural killer" cells (NK cells).

The morphological synonym for the immune system is the lymphoid system. It consists of the thymus, spleen, lymph nodes, lymphatic follicles, bone marrow and blood lymphocytes; the total number of lymphoid cells in the body is about 10¹² (R. V. Petrov, 1987). In addition to lymphocytes, numerous Proteins AND Peptides participate in immune reactions as effectors of immune processes—immunoglobulins, Complement system components, Hormones, and immune mediators.

Recently, unencapsulated accumulations of lymphoid tissue have been classified as Organs of Hematopoiesis and the Immune System: lymphoid nodules, lymphoepithelial nodules of the mucous membranes of the digestive, respiratory, urinary, and reproductive systems, as well as perivascular lymphoid nodules located around the hemocirculatory and microcirculatory beds of organs (L. V. Chernyshenko et al., 1998).

The organs of hematopoiesis and the immune system are divided into primary (or central) lymphoid organs, organa lymphoidea primaria, and secondary (or peripheral) lymphoid organs, organa lymphoidea secundaria. Primary organs include the bone marrow and thymus, while secondary organs include the spleen, lymph nodes, pharyngeal lymphoid ring (Tonsils), and the lymphoid tissue of mucous membranes and Skin.

The function of primary (central) lymphoid organs is associated with The formation of formed elements of blood and providing conditions for the antigen-independent proliferation of lymphocytes. In the Secondary Lymphoid Organs of immunogenesis, the elimination of blood cells that have completed their life cycle takes place, as well as the antigen-driven specialization of effector cells (T- and B-lymphocytes) that provide immunity. Immunity is the body's ability to rid itself of dead and degenerated cells and foreign proteins. The entire assembly of lymphoid organs and their discrete units—lymphocytes—can be viewed as a single morphofunctional system protecting the body against everything genetically foreign (R. V. Petrov, 1968; V. P. Lozovoy et al., 1974). The Organs of the immune system are affected during the course of several diseases (for example, Acquired Immunodeficiency Syndrome - AIDS, malignancies, Hodgkin's disease, lymphomas, etc.).