Primary and secondary lymphoid organs

 A number of morphologically and functionally diverse organs and tissue organs and tissue contribute to the development of immune responses .
 These organs can be distinguished by function as the primary and secondary lymphoid organs .

1. PRIMARY & SECONDARY LYMPHOID ORGANS

2. ORGANS OF THE IMMUNE SYSTEM :- A number of morphologically and functionally diverse organs and tissue organs and tissue contribute to the development of immune responses . These organs can be distinguished by function as the primary and secondary lymphoid organs .

3. Lymphoid organs - Bone marrow Thymus Spleen Lymph node Tonsils Small intestine & appendix aggregated lymphoid nodules

4. Lymphoid system: Lymphoid organs are stationed throughout the body They are concerned with the growth, development and differeciation of lymphocytes . There are structurally and functionally diverse lymphoid organs and tissues They are interconnected by the blood vessels and lymphatic vessels through which lymphocytes circulate . Based upon the functional development of the lymphatic cells the lymphoid organs are classified into 2 groups

5. Primary lymphoid organs / central - BONE MARROW - All lymphocytes arise and B – cell maturation ,,,,Thymus – T cell maturation 2 Secondary lymphoid organs / peripheral MALT - MUCOSA ASSOICATED LYMPHOID TISSUE GALT – GULT ASSOICATED LYMPHOID TISSUE SALT – SKIN ASS0ICATED LYMPHOID TISSUE

6. BONE MARROW :- Bone marrow is primary lymphoid organs . It is soft tissue within the cavity of bones It is the site of generation of all circulating blood cells in the adult , including immature lymphocytes , and is the site of B cells maturation . All the cells of immune system are initially derived form the bone marrow through a process called haematopoiesis . Immature B cells arise from lymphoid progenitors , proliferate and differentiate within t he bone marrow . Bone marrow also have stromal cells interact direct with B cells and secrets various cytokines and help in the maturation of B cells .

7. In birds – B cells development in bursa of fabricus . Bone marrow is divisible into 2 Vascular region Hematopoietic region Vascular region is the circulatory system that supplies nutrient and removes waste from actively growing blood vessels . Red bone marrow is actively involved in haematopoiesis . Res bone marrow contains titipoent cells called stem cells . The development blood cells from stem cells is called Haematopoiesis . Haematopoiesis is forms RBC , WBC – GRANULOCYTES , Lymphocytes , monocytes & platlets

8. THYMUS:- Thymus is the site of T cell differentiation and maturation . It is flat bilobed organ , situated above heart in the thorax region is lobe is encapsulated and it is divided into lobules which are separated by strands of connective tissue called trabeculae . Each lobules contains - lymphocytes & each lobule organized into two compartments Outer cortex Inner medulla

9. The cortex contains mostly immature & proliferating thymocytes , Medulla is sparly populated with thymocytes . Some of which Mature and migrate to the medulla – in medulla they learn to discriminate between self and non self fetal development and for a short time after birth . T cells leave the medulla to enter the peripheral blood circulation , through which they are transported to the secondary lymphoid organs . About 95 % of all T cells die in the thymus .

10. Besides lymphoid cells it is composed of Epithelial cells Macrophages Dendritic cells Nurse cells Hassall’s corpuscles Lymphocytes in the thymus are called thymocytes

11. Function of the thymus:- Generated and select T cells T LYMP. Cannot recognised antigen it only recognised these antigen which are bound with MSC 1 st & MHC 2 nd so T lymp must have protein which recognised MHC . TH- CD 4- MHC 2 nd + SELECTION TC – CD 8 th MHC Thus about 95 % of all T cells die in the thymus . Change in the thymus with age --

12. Secondary lymphoid organ :-

13. Red pulp is a site where defective RBC is destroyed

14. Primary lymphoid follicleS are attached TO THE PALS . Marginal zones - located at primary of PALS. They are with lymphocyte and macrophages . Antigen lymphocyte enter into the spleen antigen trapped by D.C ( Dendritic cell) which carry antigen into PALS . lymphocytes also enters into pals so activation of B and T lymphocytes with the help of dendritic cells . Means dendritic cells present antigen In MHC 2 ND to TH cells activates B cells. B & T cells migrates to primary lymphoid follicle . Primary follicle contain germinal centres . Germinal centres have specific cells knows as plasma cells. Plasma cells produced antibodies .

15. Lymph Node : - Bean shaped , encapsulated structures distributed throughout the body along the course of lymphatic vessel . They are made up of mostly B-cells , T – cells , macrophages and dendritic cells .

16. (MALT)

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