General structure
The tongue is not just a muscle, but a complex structural system. Its structure includes four main components:
- Papillae (papillae): mucosal projections on the superior and lateral surfaces.
- Salivary glands: lie within the muscle bulk, producing protein (serous), mucous, or mixed secretions.
- Lymphoid tissue: forms the lingual tonsil at the root of the tongue (part of Waldeyer's ring).
- Muscular core: provides mobility.
Histology of the tongue surfaces
The structure of the mucous membrane directly depends on the surface.
Dorsal (superior) surface Characterized by the presence of papillae. The epithelium here forms projections under which lies the lamina propria of the mucosa. A crucial feature is the absence of a submucosa. Because of this, the mucosa fuses tightly with the muscles (forming an aponeurosis) and is completely immobile.
Inferior surface The surface is smooth, with no papillae. The epithelium is non-keratinized stratified squamous. Unlike the superior part, here there is a well-defined submucosa with large blood vessels, giving the mucosa slight mobility. Interestingly, the salivary glands on the inferior surface do not lie in the submucosa, but deeper—within the muscle bulk.
Classification and structure of papillae
Every papilla consists of primary (connective tissue projection of the lamina propria) and secondary (small projections extending into the epithelium) papillae. Functionally, they are divided into two groups.
1. Mechanical (filiform and conical)
- The smallest and most numerous.
- Cover the tip and body of the tongue.
- Their apices are covered by partially keratinized epithelium (the only ones to do so).
- Give the tongue a velvety appearance and assist in the mechanical processing of food. When desquamation of keratinized scales is impaired, a white coating forms ("coated tongue").
2. Gustatory (taste) Covered by non-keratinized epithelium and contain taste buds.
- Fungiform: narrow base and wide apex, scattered among the filiform papillae on the apex and margins of the tongue.
- Foliate: parallel folds on the lateral surfaces (4–8 on each side).
- Vallate (circumvallate): the largest, arranged in a V-shape at the border of the body and root. They do not project above the surface, and are surrounded by a sulcus and a mucosal vallum. Von Ebner's protein glands empty into their sulci, and their secretion washes the receptors.
Briefly: answers to topical questions
What cell types make up a taste bud?
A taste bud consists of several cell types, totaling 30–60 cells per bud. The following cellular elements are distinguished:
- Receptor (sensory) taste epithelial cells — cells with a dark spindle-shaped nucleus, bearing microvilli with specific protein receptors on their apical side.
- Supporting epithelial cells ( sustentacular cells) — distinguished by a round nucleus and often vacuolated cytoplasm.
- Basal epithelial cells — located at the base of the taste bud.
- Perigemmal (peripheral) cells — located at the periphery of the organ.
What are the features of the histological structure of the lingual tonsil?
Histologically, the lingual tonsil represents folds of the mucous membrane, within the thickness of which lies an accumulation of lymphoid tissue. It is localized in the mucosa of the tongue root, posterior to the vallate papillae. The lymphoid tissue within it is presented in two forms:
- Lymphatic follicles — nodular accumulations.
- Parafollicular accumulations — diffuse lymphoid tissue.
The epithelium of the tonsil is infiltrated by cells participating in the immune response, specifically granulocytes, lymphocytes, and macrophages.
Which nerves provide sensory and gustatory innervation to the papillae of the tongue?
Sensory and gustatory innervation of the papillae and mucous membrane of the tongue is provided by various branches of cranial nerves depending on the zone.
- Anterior 2/3 of the tongue — general sensitivity is provided by the lingual nerve (n. lingualis), and taste by the chorda tympani (chorda tympani).
- Posterior 1/3 of the tongue and vallate papillae (papillae vallatae) — general and taste sensitivity is provided by the glossopharyngeal nerve (n. glossopharyngeus).
- Root of the tongue — innervated by the internal branch of the superior laryngeal nerve, branching from the vagus nerve (n. vagus).
Class and exam questions
What is the main difference between the dorsal and ventral surfaces of the tongue?
The dorsal surface bears papillae and lacks a submucosa (the mucosa is fixed). The ventral surface lacks papillae, has a smooth epithelium, and possesses a submucosa (the mucosa is mobile).
Which tongue papillae are keratinized?
Only mechanical papillae—filiform and conical—have partially keratinized epithelium.
Where are the glands located on the inferior surface of the tongue?
Despite the presence of a submucosa, salivary glands are absent there. They are located deeper, within the muscle tissue.
What else to study on this topic
- Histological structure of taste buds and the mechanism of taste perception.
- Characteristics of Von Ebner's glands and their connection to vallate papillae.
- Structure of the lingual tonsil and its role in immune defense.
- Differences between primary and secondary connective tissue papillae.
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