Tonsils
- Tonsils are aggregates of lymphoid tissue in the upper digestive tract.
- Capsule may be absent or incomplete in some tonsillar tissue.
- Upper digestive tract location places tonsils under and in contact with epithelium.
- Chemokine-directed organization places B cells and T cells in distinct tonsillar regions.
- Tonsils combat antigens entering through nasal and oral epithelium.
- Palatine tonsils contain crypts.
- Crypts are deep epithelial invaginations that can trap debris.
- Stratified squamous epithelium lines palatine tonsil crypts.
- Palatine tonsils contain primary and secondary lymphoid nodules.
- Connective-tissue capsule separates palatine tonsils from deeper structures.
- Pharyngeal tonsil is a single tonsil on the posterior nasopharyngeal wall.
- Posterior nasopharyngeal wall is the back wall of the upper throat behind the nasal cavity.
- Pseudostratified ciliated columnar epithelium covers the pharyngeal tonsil.
- Longitudinal pleats are folds in the pharyngeal tonsil surface.
- Pharyngeal tonsil has pleats rather than crypts.
- Pharyngeal tonsil contains primary and secondary lymphoid nodules.
- Lingual tonsil lies on the posterior third of the tongue dorsum.
- Tongue dorsum is the upper surface of the tongue.
- Stratified squamous nonkeratinized epithelium covers the lingual tonsil.
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