Functional sections and epithelial lining
The pharynx is divided into three main sections: nasal, oral, and laryngeal. The type of epithelium strictly depends on the function of the specific zone:
- Nasal region: responsible for air conduction (respiratory function); therefore, its mucosa is lined with pseudostratified ciliated epithelium, which is typical for the majority of the airways.
- Oral and laryngeal parts: have a structure characteristic of the digestive tube, as their main task is the mechanical protection of tissues during swallowing. Here, non-keratinized stratified squamous epithelium predominates.
Histological structure of the wall (oral and laryngeal parts)
The pharyngeal wall in the sections associated with digestion consists of four classic layers:
- Mucosa: includes a covering non-keratinized stratified squamous epithelium and the underlying lamina propria (lamina propria), which is formed by loose fibrous connective tissue.
- Submucosa: is located directly beneath the mucosa. This layer houses the terminal portions of mucous glands that secrete fluid to moisten the wall.
- Muscular layer: adjoins the submucosa and consists of two layers of striated skeletal muscle tissue, ensuring the voluntary act of swallowing.
- Adventitia: the outer connective tissue layer connecting the organ to surrounding neck structures.
Pharyngeal lymphoid ring (Waldeyer's ring)
The lymphoepithelial ring acts as a barrier, providing immune defense at the entrance to the respiratory and digestive tracts. It includes six tonsils:
- At the entrance to the pharynx: two palatine tonsils and one lingual tonsil.
- In the pharyngeal wall: two tubal tonsils and one pharyngeal tonsil.
Sometimes anatomists additionally distinguish a laryngeal tonsil located in the laryngeal ventricle.
The tonsils represent deep folds of the mucosa. Within the connective tissue stroma (lamina propria), lymphoid tissue is found in two morphological forms: organized lymphatic follicles (nodules) and diffuse lymphoid tissue (parafollicular clusters). Notably, the tubal tonsils contain very few follicles.
Epithelial cover and cellular infiltration of the tonsils
The epithelium covering each tonsil corresponds to the histological type of adjacent mucosal areas. The tubal tonsils are lined with pseudostratified ciliated epithelium because they are located near the nasopharynx. The pharyngeal tonsil in adult patients is covered with non-keratinized stratified squamous epithelium.
A crucial structural feature of the tonsils is cellular infiltration. The covering epithelium is actively populated by immunocompetent cells, among which lymphocytes, granulocytes, and macrophages predominate. These cells migrate into the epithelial layer, providing an immediate immune response to foreign antigens entering the mucosal surface.
Briefly: answers to topical questions
How does the epithelium of the tubal tonsils differ from that of the palatine tonsils?
The epithelium of the tubal and palatine tonsils differs in the structural type of the tissue lining.
| Characteristic | Tubal tonsils | Palatine tonsils (tonsillae palatinae) |
|---|---|---|
| Type of epithelium | Pseudostratified ciliated epithelium | Stratified squamous non-keratinized |
| Topography and features | Located closer to the nasopharynx and auditory tube | Forms 10–20 deep branching crypts, heavily infiltrated with lymphocytes, macrophages, and plasma cells |
Is there a muscularis mucosae in the pharyngeal wall?
The muscularis mucosae is absent in the pharyngeal wall. This layer appears only starting from the upper third of the esophagus. In the oral and laryngeal parts of the pharynx, the wall is represented by the following layers:
- Mucosa — includes the epithelium and lamina propria (lamina propria) formed by loose fibrous connective tissue.
- Submucosa (tela submucosa) — lies deeper than the mucosa and contains the terminal parts of mucous glands.
- Muscular layer — consists of two layers of striated skeletal muscle tissue.
- Adventitia — the outermost layer.
From which embryonic primordia does the pharyngeal epithelium develop?
The pharyngeal epithelium belongs to the anterior part of the digestive tube and has a mixed ecto-endodermal origin.
In embryogenesis, the oropharyngeal membrane plays a key role: this is the area where the ectoderm and endoderm come into contact without an intervening layer of mesoderm. It temporarily separates the primitive oral cavity and the blind end of the foregut — the pharynx. After the membrane ruptures, the germ layers mix in the perforation zone, which is why the epithelium of the anterior tube has a mixed origin.
To remember the composition of the ring, use the pairing rule: Two paired tonsils (2 palatine + 2 tubal) and two unpaired (1 lingual + 1 pharyngeal) = 6 tonsils of Pirogov's ring.
Class and exam questions
Why is the epithelium in the nasal part of the pharynx different from that in the oral part?
The nasal part performs primarily respiratory function and does not contact food. Therefore, it is lined with pseudostratified ciliated epithelium, which cleans and warms the air.
What type of muscle tissue forms the pharyngeal wall?
Unlike most parts of the gastrointestinal tract, the muscular layer of the pharynx is formed by striated skeletal muscle tissue.
In what forms is lymphoid tissue represented in the tonsils?
Lymphoid tissue is located in the mucosa as organized lymphatic follicles (nodules) and as parafollicular clusters of diffuse lymphoid tissue.
What else to study on this topic
- Topography and structure of the terminal parts of mucous glands in the submucosa.
- Structural features and localization of the laryngeal tonsil in the laryngeal ventricle.
- Morphological differences between lymphatic follicles and diffuse lymphoid tissue.
- Mechanisms of macrophage and granulocyte migration into the covering epithelium of the tonsils.
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