MH 122 Appendix

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Appendix

The appendix is a blind ending appendage to the caecum of the colon. Lymphoid tissue is abundant early in life, but diminishes with age.

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

(or mucous membrane)
- Epithelium - neither villi nor plicae circularis are present.
  - (or Enterocytes) - simple columnar cells with microvilli (or brush border).
  - (or Micro-Fold Cells) - cover nodules and have a lower profile than absorptive cells. They have small folds on their surface versus microvilli on absorptive cells).
  - - secrete mucus for lubrication.
- - fewer than in other regions of the colon.
- - abundant between the infrequent crypts.
  - Lymph nodules (,,) are common.
  - Plasma cells, lymphocytes, eosinophils and macrophages are present.
- - layer of smooth muscle.
- lymph nodules (,) may extend into the submucosa.
- two orthogonal layers of smooth muscle (inner circular and outer longitudinal).
- covers the outer surface of the appendix.