Lyphoid organs
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Primary and secondary lymphoid organs discussed. PPT is useful to Students studying X, XI, XII and B.Sc., M.Sc., Life Sciences. The teachers can also use the PPt.
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Lyphoid organs
- 1. Dr. P. VEERAMUTHUMARI, Assistant Professor of Zoology, V.V.Vanniaperumal College for Women, Virudhunagar – 626 001 veeramuthumari@vvcollege.org;muthusdream@gmail.com 7/14/2020 1
- 2. LYPHOID ORGANS The lymphoid organs in the human body includes the spleen, lymph nodes, bone marrow, thymus and lymph tissue. The lymphatic system is a network of tissues and organs that help to clear toxins, waste and other unwanted materials present in the human body. The primary function of the lymphatic system is to transport lymph, a fluid containing infection to fighting with white blood cells, throughout the body. https://www.google.com/search?q=define+ly mphoid+organs&source=lnms&tbm=isch&sa 7/14/2020 2
- 3. PRIMARY LYMPHOID ORGANS (a) Bone marrow (b) Thymus In primary lymphoid organs, immature lymphocytes differentiate to mature ones into an antigen sensitive lymphocytes and after maturation, lymphocytes migrate to secondary lymphoid organs. 7/14/2020 3
- 4. (a) Bone Marrow: It is the main lymphoid organ, where all the lymphocytes and all the body cells are produced and T-lymphocytes are developed. Bone marrow is soft, gelatinous tissue that fills the medullary cavities, the centers of bones. such as hip and thigh bones. The two types of bone marrow are red bone marrow, known as myeloid tissue, and yellow bone marrow, or fatty tissue. The major function of bone marrow is to generate blood cells. Bone marrow contains two main types of stem cells. Hematopoietic stem cells, found in red marrow, are responsible for the production of blood cells. The stem cells that carry oxygen through out the body, the white blood cells that fight infections, and initiate the platelets that help with blood clotting. 7/14/2020 4
- 5. (b) Thymus: It is a lobed organ, The thymus is a small, irregular-shaped gland in the top part of the chest, just under the breastbone and between the lungs. It is located in an area of the body called the mediastinum. The thymus is part of both the lymphatic system and the endocrine system. It is large at the time of birth but with age, the size keep on reducing and becomes very small by attaining puberty. Growth and maturation of T- lymphocytes takes place in thymus only. Both bone marrow and thymus provide micro-environments for the development and maturation of T- lymphocytes. 7/14/2020 5
- 6. SECONDARY LYMPHOID ORGANS These organs provide the sites for the interaction of lymphocytes with the antigen, which then proliferate to become effector cells. These are of following types: (a) Spleen (b) Lymph nodes (c) Mucosal associated Lymphoid Tissue (MALT) Peyer’s patches of small intestine and appendix are also some of the secondary lymphoid organs. 7/14/2020 6
- 7. (a) Spleen: Spleen, organ of the lymphatic system located in the left side of the abdominal cavity under the diaphram, the muscular partition between the abdomen and the chest. It is a large bean-shaped organ containing lymphocytes and phagocytes. It filters the blood by trapping the pathogens in it. The white pulp of the spleen contains typical lymphoid elements, such as plasma cells, lymphocytes, and lymphatic nodules, called follicles in the spleen. Germinal centre in the white pulp serve as the sites of lymphocyte production. Similar to the lymph nodes, the spleen reacts to microorganisms and other antigens that reach the bloodstream by releasing special phagocytic cells known as macrophages. Splenic macrophages reside in both red and white pulp, and they serve to remove foreign material from the blood and to initiate an immune reaction that results in the production of antibodies. 7/14/2020 7
- 8. (b) Lymph Nodes: These are small solid structures located at different points along the lymphatic system. Their function is to trap the microorganisms or other antigens, that enter the lymph and tissue fluid. Therefore, the antigens trapped in the lymph nodes are responsible for the activation of lymphocytes present there and cause the immune response. Lymph nodes- These are small, bean- shaped structures which produce and store cells, specialized in fighting infections. They are a part of the lymphatic system. The lymphatic system is part of the vascular system and an important part of the immune system, composed of a large network of lymphatic vessels that carry a clear fluid called lymph directionally towards the heart. 7/14/2020 8
- 9. (c) Mucosal Associated Lymphoid Tissue (MALT): The mucosa-associated lymphoid tissue (MALT), also called mucosa-associated lymphatic tissue, is a diffuse system of small concentrations of lymphoid tissue found in various submucosal membrane sites of the body, such as the gastrointestinal tract, nasopharynx, thyroid, breast, lung, salivary glands, eye, lining of main tracts in the body like respiratory, digestive, urogenital tracts and skin. It constitutes about 50% of the lymphoid tissue in human body. MALT is populated by lymphocytes such as T cells and B cells, as well as plasma cells and macrophages, each of which is well situated to encounter antigens passing through the mucosal epithelium. In the case of intestinal MALT, M cells are also present, which sample antigen from the lumen and deliver it to the lymphoid tissue. There are three types of situations in which MALT is present- Tonsils, Appendix and Small intestine area. Peyer's patches are small masses of lymphatic tissue found throughout the ileum region of the small intestine. Also known as aggregated lymphoid nodules, they form an important part of the immune system by monitoring intestinal bacteria populations and preventing the growth of pathogenic bacteria in the intestines. 7/14/2020 9
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