4.Lymphoid system

4.Lymphoid system

1. Lymphoid tissue

   • Important of Lymphoid tissue
     • 1. a place for lymphocyte poliferation(newly formed WBC from bone marrow): -have immunological education - contribute to other immune response
   • classification
     • Central lymphid tissue
       • 1. produce immature lymphocytes(from bone marrow) 2. become mature lymphocytes after 'immunological education' in thymus
       • Location
         • Thymus-immunological education center
           • 1.The immature lymphocytes from bone marrow to thymus become mature 2.enter the blood stream and distributed to other lymphoid tissue.
           • Structure
             • 1. loose collagenous capsule surround the thymus
             • lobulated organ
               • 1.short inter-lobular septa containing blood vessels
               • each lobule(cortex + medulla) composed of cortex
                 • 1. reason:packed with large number of medulla and lymphocyte(closely packed lymphocytes can mask significant number of epithelial cells-epithelioreticular cells)
       • Functions
         • lymphocyte differentiation
           • aims: develop the ability to recognize non-self antigens from self 1.Bone marrow: B lymphocytes can produce antibodies 2. Thymus: antigen presenting cells
         • colonize the peripheral sited as diffuse, encapsulated
     • peripheral lymphoid tissue
       • 1. for organized mature lymphocytes 2. contain a series of filter: monitor the contents of ECF(e.g. lymph blood)  3.Foreign antigens and further the immune response take place: -Lymph node: filter the lymph -Spleen: monitor the erythrocytes
       • Location
         • Non-encapsulate lymphoid tissue
           • Gut-associated lymphoid tissue
             • 1. Lymphoid tissue in mucosa of digestive tract       e.g. peyer patches(group of lymphoid follicle)        e.g. lymphoid in ilum
           • Bronchus-associated lymphoid tissue
             • 1. lymphoid tissue in mucosa of respiratory tract e.g. lymphoid tissue in branchi or branchioles
             • have lymphoid
               • large amount lymphocyte aggregate
         • encapsulate lymphoid tissue(lymphoid organ)
           • encapsulated by dense connective tissue
           • Lymph-node
             • 1. filter the lymph How?? (MOA)Lymph enter from afferent lymphatic to lymph-node / filtered lymph return back to lymphatic system through efferent lymphatic
             • Functions
               • 1. non-specific filtration of non-self by phagocytic activity of macrophages 2. aggregation, poliferation and activation of T & B lymphocytes
             • structure
               • a kidney shape
                 • with a concavity on one side-hilum
               • Cortex(outer region)
                 • contains lymphoid nodules
                   • -with germinal center(aggregate large number of lymphocytes with paler nuclei)
               • Medulla(center area)
                 • contains medullary cord
                   • in the center area: formed by irregular cords & clumps of lymphoid cells.
           • Spleen(secondary lymphoid organ)
             • 1. monitor erythrocytes 2. receive rich blood supply via a single artery(splenic artery: it is drained by splenic vein into splenic portal system)
             • location
               • In the left upper part of abdomin
             • Function
               • 1. production of immunological response against blood borne antigens 2. removal of particulate matter, aged and defective cells
             • structure
               • enclosed by a thick capsule of fibrous tissue
                 • contains a few smooth muscle fibres
               • Trabeculae(connective tissue)
                 • 1. provide internal support for the spleen 2. carry the blood vessels into the spleen
                 • intensely vascular
                   • may contain sinusoid and erythrocytes
                     • Red pulp
                       • with splenic cord
                         • it has reticular fiber cells, macrophages, blood cells and plasma cell.
                       • splenic sinusoid
                         • 1. lined by elongated endothelial cells(surrounded by basement membrane and reticular fibers)
                   • Packed with numerous lymphocytes
                     • White pulp
                       • associated with arteries
                       • composed of periarterial lymphatic sheath(PALS)
                       • lymphatic nodules

2. Lymphocytes

   • strongly basophilic nucleus
     • surrounding by (thin) pale staining of cytoplasm
   • Types
     • B lymphocytes
       • 1. can respond foreign substances after leave the BM
     • T lymphocytes
       • 1. further need immunological education in peripheral lymphoid tissue