MHS 221 Appendix

Appendix

This appendix has abundant lymphoid tissue. There are very few crypts and the lamina propria is the dominant feature of the mucosa.

The appendix is composed of the four layers characteristic of the gastrointestinal tract.

• Mucosa (or mucous membrane)
  • Epithelium - neither villi nor plicae circularis are present.
    • Absorptive Cells (or Enterocytes) - simple columnar cells with microvilli (or brush border).
    • M-Cells (or Micro-Fold Cells) - cover nodules and have a lower profile than absorptive cells (small folds on their surface versus microvilli on absorptive cells).
    • Goblet Cells - secrete mucus for lubrication.
  • Crypts - very few in number.
  • Lamina Propria - comprises almost the entire mucosa.
    • Nodules (#1,#2,#3,#4) fill the lamina propria.
    • Plasma cells, lymphocytes, eosinophils and macrophages are present (#1,#2,#3).
• Submucosa - nodules may extend into the submucosa..
• Muscularis Externa - two orthogonal layers of smooth muscle (inner circular and outer longitudinal).
• Serosa - covers the outer surface of the appendix.