lymphoid organs

Examples of lymphoid organs in the following topics:

• Lymphoid Tissue

  • Lymphoid tissue consists of many different organs playing a role in the production and maturation of lymphocytes in the immune response.
  • The tissues of lymphoid organs are different than the tissues in most other organ systems because different tissues within the system vary considerably based on cell cycle proliferation of lymphocytes.
  • The central or primary lymphoid organs generate lymphocytes from immature progenitor cells, such as lymphoblasts.
  • Secondary or peripheral lymphoid organs maintain mature naive lymphocytes until an adaptive immune response is initiated.
  • Mature lymphocytes will then recirculate between the blood and the peripheral lymphoid organs until they encounter their specific antigen, where they will perform their immune response functions.

• Structure of the Lymphatic System

  • The lymphatic system consists of lymphatic vessels and associated lymphoid organs.
  • Lymphatic organs are the site of many important functions for the immune system.
  • Lymphoid tissue is found in many organs, particularly the lymph nodes, as well as in the lymphoid follicles in the pharynx, such as the tonsils.
  • Lymph nodes are found 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.
  • Describe how the lymphatic system consists of lymphatic vessels and associated lymphoid organs

• Cells and Organs of the Immune System

  • The immune system includes primary lymphoid organs, secondary lymphatic tissues and various cells in the innate and adaptive immune systems.
  • The key primary lymphoid organs of the immune system include the thymus and bone marrow, as well as secondary lymphatic tissues including spleen, tonsils, lymph vessels, lymph nodes, adenoids, skin, and liver.
  • The red bone marrow is a key element of the lymphatic system, being one of the primary lymphoid organs that generate lymphocytes from immature hematopoietic progenitor cells.
  • Lymphoid tissue is found in many organs, particularly the lymph nodes.
  • Recognize the cells and organs of the immune system and their functions

• Development of the Dual Lymphocyte System

  • During this process, all lymphocytes originate from a common lymphoid progenitor before differentiating into their distinct lymphocyte types.
  • B cells mature into B lymphocytes in the bone marrow, while T cells migrate to, and mature in, a distinct organ called the thymus.
  • Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the spleen and lymph nodes) where they survey for invading pathogens and/or tumor cells.
  • All lymphocytes originate during this process from a common lymphoid progenitor before differentiating into their distinct lymphocyte types.

• 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 that are located in the pharynx.  
  • They function similarly to other types of secondary lymphoid organs and also act to capture antigens from respiratory tract pathogens.
  • The tonsils are made of secondary lymphoid tissue, but are also covered with an epithelium that is characteristic of the part of the tonsil that they are located in.
  • The secondary lymphoid tissue within the tonsils functions similarly to 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 are also the reason for much of the damage in cell-mediated hypersensitivity, autoimmune disorders, and organ transplant rejection.
  • All lymphocytes originate, during this process, 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.

• Cardiovascular and Lymphatic System Defenses

  • Lymphatic organs play an important part in the immune system, having a considerable overlap with the lymphoid system.
  • Lymphoid tissue is found in many organs, particularly the lymph nodes, and in the lymphoid follicles associated with the digestive system such as the tonsils.
  • Lymphoid tissues contain lymphocytes, but they also contain other types of cells for support.
  • The first attach invading micro organisms directly while others produce antibodies that circulate in the blood and attack them.
  • When micro-organisms invade the body, or the body encounters antigens (such as pollen), antigens are transported to the lymph.

• Development of the Immune System

  • The old model: Lymphoid vs Myeloid ( and ).
  • This model of lymphopoiesis had the virtue of relative simplicity and agreement with nomenclature and terminology; also, it is essentially valid for the favorite lab animal, the mouse. 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.
  • NK cells Dendritic cells (lymphoid lineage; DC2) Progenitor B cells Pro-B cells => Early Pro (or pre-pre)-B cells => Late Pro (or pre-pre)-B cells Large Pre-B cells => Small Pre-B cells Immature B cells B Cells => (B1 cells; B2 cells) Plasma cells Pro-T cells T-cells.
  • In fact, many of the infections acquired by neonates are caused by low virulence organisms like Staphylococcus and Pseudomonas.