primary lymphoid organ

Examples of primary lymphoid organ in the following topics:

• Lymphoid Tissue

  • The lymphoid tissue may be primary or secondary depending upon its stage of lymphocyte development and maturation.
  • Central or primary lymphoid organs generate lymphocytes from immature progenitor cells such as lymphoblasts.
  • The thymus gland and bone marrow contain primary lymphoid tissue where B and T cells are generated.
  • Besides generation, primary lymphoid tissue is the site where lymphocytes undergo the early stages of maturation.
  • The thymus and bone marrow are primary lymphoid tissue, while the lymph nodes, tonsils, and spleen are secondary lymphoid tissue.

• Thymus

  • The thymus is a specialized organ that "educates" T cells or T lymphocytes, which are part of the adaptive immune system.
  • The thymus is a specialized organ of the immune system.
  • It consists of primary lymphoid tissue, which provides a site for the generation and maturation of T lymphocytes, critical cells of the adaptive immune system.
  • The organ enlarges during childhood into adolescence and begins to atrophy at puberty due to hormonal changes.

• Development of the Immune System

  • In fact, many of the infections acquired by neonates are caused by low-virulence organisms like staphylococcus and pseudomonas.
  • There is evidence that these steroids act directly not only on the primary and secondary sexual characteristics, but also affect the development and regulation of the immune system.
  • The lymphoid vs. myeloid model of lymphopoiesis has the virtue of relative simplicity and agreement with nomenclature and terminology, as well as validity for tests with mice. pHSC pluripotent, self-renewing, hematopoietic stem cells give rise to MPP multipotent progenitors (these give rise to ELP, or PRO, prolymphocytes); early lymphoid progenitors; and finally to the CLP common lymphoid progenitor, a cell type fully committed to the lymphoid lineage. pHSC, MPP and ELP cells are not fully committed to the lymphoid lineage because if one is removed to a different location, it may differentiate into non-lymphoid progeny.
  • However, CLP are committed to the lymphoid lineage.
  • This revised flowchart indicates multi-lymphoid progenitor, early thymic progenitor, lymphoid extrusion, CD4 and CD8, monocyte/macrophate, myeloid extrusion, and T-cells.

• Structure of the Lymphatic System

  • The lymphatic system consists of lymphatic vessels and associated lymphoid organs.
  • Lymphoid tissue is found in many organs including the lymph nodes, as well as in the lymphoid follicles in the pharynx such as the tonsils.
  • Lymphoid tissues contain lymphocytes (a type of highly differentiated white blood cell), but they also contain other types of cells for structural and functional support, such as the dendritic cells, which play a key role in the immune system.

• WBC Formation

  • The daughters are the myeloid and lymphoid progenitor cells, which cannot self renew but differentiate into various myeloid leukocytes and lymphocytes respectively.
  • When bone marrow develops, it eventually assumes the task of forming most of the blood cells for the entire organism.
  • However, maturation, activation, and some proliferation of lymphoid cells occurs in lymphoid organs (spleen, thymus, and lymph nodes).
  • It may cause these organs to hypertrophy and increase in size substantially.
  • During fetal development, the liver functions as the main haematopoetic organ since bones and marrow develop later.

• Tonsils

  • The tonsils are small masses of secondary lymphoid tissue located in the pharynx.
  • They function similarly to other types of secondary lymphoid organs and also capture antigens from respiratory tract pathogens.
  • The tonsils are made of secondary lymphoid tissue and covered with an epithelium characteristic of the part of the body where they are located.
  • The secondary lymphoid tissue within the tonsils functions like the same type of the tissue in lymph nodes.

• Lymphoid Cells

  • Lymphocytes develop from lymphoblasts (differentiated blood stem cells) within lymphoid tissue in organs such as the thymus.
  • Helper T cells (CD4s) facilitate the organization of immune responses.
  • Cytoxic T cells cause much of the damage associated with cell-mediated hypersensitivity, autoimmune disorders, and organ transplant rejection.
  • All lymphocytes originate from a common lymphoid progenitor cell known as a lymphoblast, before differentiating into their distinct lymphocyte types.
  • Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs, where they survey for invading pathogens and cancer cells.

• Development of Blood

  • Commonly known as white blood cells, they are derived from common lymphoid progenitors.
  • The lymphoid lineage is primarily composed of T-cells and B-cells.
  • When bone marrow develops, it eventually assumes the task of forming most of the blood cells for the entire organism.
  • However, maturation, activation, and some proliferation of lymphoid cells occurs in secondary lymphoid organs, such as the spleen, thymus, and lymph nodes.
  • Angiogenesis is generally responsible for colonizing individual organ systems with blood vessels, whereas vasculogenesis lays down the initial pipelines of the network.

• Maturation of B Cells

  • Immature B cells are produced in the bone marrow and migrate to secondary lymphoid tissues where some develop into mature B cells.
  • After reaching the IgM+ immature stage in the bone marrow, these immature B cells migrate to secondary lymphoid tissues (such as the spleen, lymph nodes, Peyer's patches, etc.) where they are called transitional B cells, and some of these cells differentiate into mature B lymphocytes.
  • In the bone marrow (the central lymphoid organ), central tolerance is produced.
  • Other functions for B cells include antigen presentation, cytokine production, and lymphoid tissue organization.

• Spleen

  • The spleen is the largest distinct organ of the lymphatic system.
  • White pulp is secondary lymphoid tissue that is similar to that in the adenoid tonsils.
  • The splenic artery forms its primary blood supply.
  • However, it still shares the same blood supply as the foregut organs in the abdominal cavity.
  • The primary function of the spleen is blood filtration.