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