Immunology Chapter 2

==Primary Lymphoid Organs:==

sites for generation of lymphoid cells

^^Bone Marrow^^

• site of hematopoiesis

^^Thymus^^

• site of T cell maturation
• bi-lobed organ with each lobe divided into several smaller lobules
• thymic involution (degeneration) = starts at puberty and continues
  • thymus is progressively replaced with adipose tissue
  • thymus largest in children
  • decrease thymus = decrease T cells
• each lobule contains 2 major areas:

%%1.) cortex%%

• immature thymocytes (pre-T cells)
• cells move toward medulla as they mature

%%2.) medulla%%

• mature T cells
• move out of thymus into bloodstream and lymphatic system
• Hassall’s corpuscles = tightly packed degenerating epithelial cells wrapped around each other forming a whorl

Spread throughout thymus:

• epithelial cells (structural)
• dendritic cells (antigen presenting for mature thymocytes)
• macrophage (antigen presenting and degradation)

==Secondary Lymphoid Tissue:==

^^Lymph Nodes^^

• %%lymph%% = fluid drained from tissues
  • lymphatic system → lymph → lymph nodes → bloodstream → thoracic duct → superior vena cava
• %%afferent lymphatic vessels%% = lymph in lymph nodes
• %%efferent lymphatic vessels%% = lymph out lymph nodes

Structure of Lymph Nodes

• surrounded by fibrous capsule
• lymphoid follicles:
  • primary lymphoid follicles = not activated, contains naive B cells
  • secondary lymphoid follicles = activated, contains germinal centers that have B cells
  • follicular dendritic cells = antigen presenting B cells

^^Spleen^^

• peripheral lymphoid organ located behind stomach
• %%trabecular artery%% = brings blood to spleen
• %%red pulp%% = empties blood
  • contains erythrocytes, macrophage, dendritic cells, plasma cells, and lymphocytes
  • dendritic and macrophage = captures antigen from blood, ingest, and degrade used RBC
• %%white pulp%%
  • contains PALS
  • fluid coming out of blood vessel that contains antigen is exposed to T cells becomes activated
  • germinal center = activated B cells

^^Mucosal Associated Lymphoid Tissue (MALT)^^

• examples = tonsils, adenoid, appendix, Peyer’s Patches
• contain lymphoid follicles → germinal centers
• dendritic cells = capture antigen and present it to cells in follicle or migrate the lymph carrying the antigen away from tissue to lymph nodes

Peyer’s Patch

• antigens enter through M cells (contains small microfolds that has high surface area to absorb antigens and transport across epithelial layer into Peyer’s Patch)
• lymphocytes → Peyer’s Patch → venules → efferent lymphatics

==Summary==

• spleen collects antigen in blood
• lymph nodes collects antigen from tissues
• lymphocytes becomes activated and begin specific immune response