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:$$$Spread throughout thymus:$$

• 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$$$Structure of Lymph Nodes$$

• 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$$$Peyer’s Patch$$

• 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