MHS 210 Thymus

Thymus

Thymus is an encapsulated organ where T-cells proliferate and mature behind the blood-thymus barrier.

This slide has good examples of macrophages.

• Capsule - thin connective tissue surrounding the thymus that extends trabeculae inward forming incomplete lobules.
• Cortex - outer darker, region of small lymphocytes.
  • T Lymphocytes - tightly packed, small nuclei of condensed chromatin
  • Epithelial Reticular Cells - large cells with oval nuclei and lightly stained cytoplasm with processes. Their nuclei have euchromatin and a prominent nucleolus.
  • Macrophages (#1,#2,#3) - large cells that phagocytize T cells marked for removal. Many of the macrophages contain phagocytized lymphocytes with pyknotic nuclei.
  • Mast Cells - round cells with oval nuclei and granules stained a bright red.
  • Cortical Capillaries (cross-section and longitudinal) - the site of the blood-thymus barrier.
• Medulla - inner, lighter region of larger lymphocytes.
  • Epithelial Reticular Cells - large cells with oval nuclei and lightly stained cytoplasm.
  • Hassall's Corpuscle (#1,#2,#3) - closely packed, concentrically arranged epithelial reticular cells.
  • Post Capillary Venules (#1,#2) - have a wide lumen and the endothelial nuclei bulge into the lumen. This is the site where lymphocytes exit the thymus.