Histology of the Tonsils

Overview & Waldeyer's Ring

Low-Power Architecture (H&E ×47)

• SSE — stratified squamous epithelium covering the free surface
• TC — tonsillar crypts (deep invaginations of the epithelium into the connective tissue)
• L — masses of lymphatic tissue occupying the mucosa
• MG — mucus-secreting glands at the base of the crypts

Layer-by-Layer Histological Description

1. Surface Epithelium

• The palatine and lingual tonsils are covered by non-keratinized stratified squamous epithelium (SSE).
• The pharyngeal tonsil is covered by pseudostratified ciliated columnar (respiratory) epithelium with patches of stratified squamous epithelium.

2. Tonsillar Crypts

• The surface epithelium dips deep into the underlying connective tissue, forming branching, invaginated pockets called tonsillar crypts.
• The palatine tonsil has 10–20 primary crypts; these expand surface area enormously for antigen sampling.
• Crypt epithelium is characteristically heavily infiltrated by lymphocytes — so densely, in fact, that the epithelium may be almost impossible to identify. This is called lymphoepithelium or reticulated epithelium.
• The lamina propria–epithelial boundary is disrupted in these areas; the collagen band at the interface appears as small fragments, and lymphoid nodules appear to have literally grown into the epithelium.

3. Lymphoid Nodules (Follicles)

• Beneath and between the crypts lie numerous lymphatic nodules (follicles) within the lamina propria/mucosa.
• The nodules are so numerous and closely packed that they tend to merge with one another.
• Many nodules have germinal centers (GC) — pale, eosinophilic zones containing activated B lymphocytes (centroblasts and centrocytes), follicular dendritic cells, and macrophages (tingible-body macrophages).
• The dark-staining mantle zone (corona) of small, resting lymphocytes surrounds the germinal center.

4. Interfollicular (Parafollicular) Zone

• Between the nodules lies the interfollicular (T-cell–rich) zone, containing:
  • Small T lymphocytes
  • Postcapillary high endothelial venules (HEVs) — specialized vessels that facilitate lymphocyte recirculation into the tissue
  • Plasma cells and occasional eosinophils

5. Submucosa

• Deep to the lymphoid tissue is a layer of dense irregular connective tissue (submucosa, labeled S in the micrograph).
• Mucous and seromucous glands are present here, with ducts opening at the base of the crypts; their secretions help flush debris from the crypts.
• There is no capsule on the free (mucosal) surface; a fibrous pseudocapsule forms only on the deep/lateral aspect, separating the tonsil from surrounding muscle.

6. Blood & Lymphatic Vessels

• Afferent lymphatic vessels are absent — antigens arrive directly via the overlying epithelium/crypts, not via afferent lymphatics (unlike lymph nodes).
• Efferent lymphatic vessels drain lymph away from tonsillar tissue.
• A rich blood supply enters through the pseudocapsule.

Higher-Magnification Detail (H&E ×47 and ×365)

• The left side shows a clear boundary between epithelium and lamina propria, with a thin band of collagen fibers (CF) at the interface and only a few lymphocytes entering the epithelium.
• The right side demonstrates the striking lymphocytic invasion: isolated islands of epithelial cells (Ep) appear completely surrounded by lymphocytes; the collagen band is disrupted into fragments, and the nodule has grown into the epithelium, obliterating the normal boundary.

Gross-to-Microscopic Anatomy

Comparison: Tonsils vs Lymph Nodes

Functional Significance