Special Histology and Embryology: Practical Manual - V. K. Napkhanyuk 2001

Digestive System
Anterior Segment of the Digestive System
Tongue

The tongue (lingua) is a muscular organ that, In addition to participating in mechanical food Processing and swallowing, also provides articulation (sound production) and taste sensation.

The tongue is composed of striated Muscle covered by a mucous membrane.

Striated muscle fibers interweave with one another. They are arranged in the body of the tongue in three mutually perpendicular directions, As a result of which some fibers in the section appear cross-cut, while others appear longitudinally cut. Bundles of muscle fibers cut longitudinally resemble strands, whereas those cut transversely look like oval or polygonal structures gathered into groups.

The endomysium is located between the striated muscle fibers. These are thin layers of Connective Tissue that bind the muscle fibers together. The endomysium can be distinguished by the shape of the nuclei of its connective tissue Cells: they are narrower and more intensely stained than the nuclei of the striated muscle fibers.

Blood Vessels and nerves run through the wider layers of connective tissue between the bundles of muscle fibers (the perimysium).

The muscular body is covered by a mucous membrane (tunica mucosa). It is formed by stratified squamous epithelium and an underlying lamina propria consisting of loose connective tissue, in which numerous small Blood Vessels can be distinguished.

On the dorsal surface of the tongue, the mucous membrane forms numerous projections known as papillae. There are four types of papillae: filiform, fungiform, foliate, and circumvallate.

The ventral surface of the tongue is smooth. The submucosa, which is present in other PARTS OF THE digestive tract, is absent in the tongue; therefore, the perimysium of the Muscles merges directly into the connective tissue of the lamina propria and is immovably fused with it.

Filiform papillae (papillae filiformes) are the most numerous. They are formed by projections of connective tissue covered by stratified squamous epithelium. The outer layers of the epithelium, particularly near the apex of the papilla, undergo keratinization, and the keratinized scales—in which remnants of degenerated nuclei can still be discerned—cover the papillae in a shingle-like manner.

The connective tissue of the papilla forms additional invaginations, or projections, into the deep epithelium, known as secondary papillae.

The section sometimes passes not longitudinally through the papilla, but obliquely or even transversely; in such cases, the filiform papillae in the specimen may exhibit a variety of shapes, including rounded ones detached from the tongue.

Fungiform papillae (papillae fungiformes) differ distinctly in shape from the conical filiform papillae: being broader at the apex and narrower at the base, they truly resemble mushrooms.

Like the filiform papillae, they are formed by an evagination of the lamina propria and are covered by a thin layer of stratified squamous epithelium without any signs of keratinization. Their surface is smooth, lacking any projections unlike the filiform papillae. The connective tissue forms numerous finger-like evaginations into the epithelium (secondary papillae) and is highly vascularized. Taste buds are occasionally found in the epithelium of the lateral walls of the fungiform papillae. They appear as oval structures composed of elongated epithelial cells.

Circumvallate papillae (papillae vallatae) are located between the body and the ROOT of the tongue. They are larger in size (1–3 mm in diameter) than the others.

The core of the papilla is composed of connective tissue lined with stratified squamous epithelium. In the epithelium of the upper part of the papilla, the connective tissue forms numerous short projections—secondary papillae.

The circumvallate papilla is embedded by its entire mass into the thickness of the mucous membrane of the tongue. It is surrounded by a deep groove known as a moats. On the opposite side of the moat, the mucous membrane forms a wall (vallum) that encircles it.

Strands of smooth muscle cells are located in the connective tissue of the circumvallate papilla and the surrounding wall. Upon their contraction, the moat closes.

Taste buds are located in the epithelium of the lateral walls of the papilla and the opposing walls of the moat. They are oval in shape and easily noticeable due to their lighter staining compared to the adjacent cells.

Tubular protein (serous) glands are located beneath the papillae in the intermuscular connective tissue; their secretion pours through an excretory duct into the depth of the moat. Near the serous glands, alveolar-tubular mucous glands can be observed; they have a slightly lighter coloration than the protein glands. Their excretory ducts open onto The surface of the tongue.

During eating, food particles enter the moat and are retained near the taste receptors (taste buds) due to the contraction of the smooth muscle Cells of the papilla and the wall. Afterward, the secretion of the glands flushes the moat, allowing a new portion of food to enter.

Foliate papillae (papillae foliatae). Foliate papillae are arranged in several rows on the lateral surfaces of the tongue. Like the other papillae of the tongue, they are formed by an evagination of the lamina propria and are covered by stratified squamous epithelium.

The lamina propria of the papilla forms three deep secondary papillae that project into the epithelium.

The epithelium covers the connective tissue of the secondary papillae in an even layer. Each foliate papilla is separated from adjacent ones by a deep groove. Oval taste buds are located in the epithelium lining the lateral surfaces of the foliate papillae. They face the groove and function as the receptors of The ORGAN OF TASTE. In preparations, they are easily distinguished due to the lighter staining of their cells.

Groups of small alveolar glands that secrete a proteinaceous substance are located in the connective tissue permeating the muscular body of the tongue, beneath the papillae. In the specimen, they appear as small, rounded vesicles formed by a single-layered epithelium. The ducts of these glands lead into the groove between the papillae.

Taste buds (caliculi gustatorii) form the peripheral part of the gustatory analyzer (micrograph 23).

Each taste bud spans almost the entire thickness of the epithelium. It originates at the basement membrane but does not reach the epithelial surface, leaving a small depression known as the taste pit. The pit opens into a taste pore formed by the superficial cells of the covering epithelium. Under high magnification, it is evident that taste buds consist of tightly packed cells. They are elongated so that their bases and apices converge at the poles of the bud. As a rule, Two Types of cells are distinguished: wide cells with light nuclei and narrow cells with dark nuclei. Some cells terminate apically with elongated cuticular microvilli (hairs) that project into the taste pit.

The narrow cells with dark nuclei are gustatory sensory epitheliocytes with microvilli (epitheliocytus sensorius gustatorius). The wide cells with light nuclei are supporting epitheliocytes (epitheliocytus sustentaculi).

Slide 2. Section of the tongue showing filiform and fungiform papillae (Figs. 36, 37).

Low power. Examine and draw the slide. Locate the filiform and fungiform papillae, paying attention to differences in their shape, The Structure of the covering epithelium (which is partially keratinized in filiform papillae), and the absence of a submucosa. In a filiform papilla, identify the lamina propria of the mucous membrane, which forms secondary papillae, as well as striated muscle fibers.

Label the following on the drawing: A. Filiform papilla: 1) Cytology/practical/35.html">Stratified squamous keratinized epithelium; 2) lamina propria of the mucous membrane; 3) blood vessels; 4) primary connective tissue papilla; 5) secondary papillae; 6) striated muscle fibers. B. Fungiform papilla: 1) stratified squamous epithelium; 2) lamina propria of the mucous membrane; 3) blood vessels; 4) primary connective tissue papilla; 5) secondary papillae; 6) striated muscle fibers.

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Fig. 36. Section of the tongue. Filiform papillae. Hematoxylin and eosin stain. ×40:

1 — stratified squamous keratinized epithelium; 2 — lamina propria of the mucous membrane; 3 — blood vessels; 4 — primary connective tissue papilla; 5 — secondary papillae; 6 — striated muscle fibers

Fig. 37. Section of the tongue. Fungiform papillae. Hematoxylin and eosin stain. ×40:

1 — stratified squamous epithelium; 2 — lamina propria of the mucous membrane; 3 — blood vessels; 4 — primary connective tissue papilla; 5 — secondary papillae; 6 — striated muscle fibers

Slide 3. Section of the tongue. Vallate papilla of the tongue (Fig. 38).

Low power. Examine and draw the slide. At this magnification, locate the connective tissue core of the papilla and the stratified squamous epithelium covering it. Note the minimal Development of the keratinized layer and the presence of tall secondary connective tissue papillae. Thickening of the epithelium is observed on the lateral surfaces of the papilla, extending to the floor of the surrounding moat and further onto the wall of the surrounding wall (vallum). Blood vessels run within the connective tissue core of the papilla. Pale-staining taste buds can be observed deep within the moat.

Label the following on the drawing: 1) stratified squamous epithelium; 2) lamina propria of the mucous membrane; 3) secondary papillae; 4) moat (crypt); 5) wall (vallum); 6) taste buds; 7) serous Salivary Glands; 8) mucous salivary glands; 9) striated muscle fibers.

Fig. 38. Section of the tongue. Vallate papilla of the tongue. Hematoxylin and eosin stain. ×140:

1 — stratified squamous epithelium; 2 — lamina propria of the mucous membrane; 3 — secondary papillae; 4 — moat; 5 — wall; 6 — taste buds; 7 — serous salivary glands; 8 — striated muscle fibers

Slide 4. Section of the tongue. Foliate papillae of the tongue (Figs. 39, 40).

Low power. Examine and draw the slide. Locate the foliate papillae, which are arranged in groups separated by narrow clefts. They are covered with stratified squamous epithelium. The core of the papilla is formed by an extension (primary papilla) of the lamina propria of the mucous membrane. The excretory ducts of serous salivary glands open into the clefts separating the foliate papillae. Taste buds are located on the lateral surfaces of the papillae.

High power. Examine a taste bud. It has an ellipsoidal shape and spans the entire thickness of the epithelial layer of the papilla. It consists of 40–60 tightly packed cells.

Fig. 39. Section of the tongue. Foliate papillae of the tongue. Hematoxylin and eosin stain. ×140:

1 — lamina propria of the mucous membrane; 2 — secondary papillae; 3 — stratified squamous epithelium; 4 — taste buds; 5 — cleft (moat); 6 — striated muscle fibers; 7 — cross-sectioned striated muscle fibers; 8 — serous salivary glands; 9 — gland duct

Label the following on the drawing: A. Foliate papillae of the tongue: 1) lamina propria of the mucous membrane; 2) secondary papillae; 3) stratified squamous epithelium; 4) taste buds; 5) cleft; 6) striated muscle fibers; 7) serous salivary glands; 8) gland duct. B. Taste bud: 1) taste pit; 2) microvillus (Hair); 3) taste bud cells; 4) epithelium of the foliate papilla; 5) lamina propria of the foliate papilla.

Fig. 40. Section of the tongue. Taste bud of a foliate papilla. Hematoxylin and eosin stain. x 400:

1 — taste pore; 2 — microvilli (hairs); 3 — taste bud cells; 4 — epithelium of the foliate papilla; 5 — lamina propria of the mucosal layer of the foliate papilla

Control Questions

1. Histogenesis of the Digestive System Organs.

2. General plan of the microscopic STRUCTURE OF THE digestive tube.

3. Constituent Components of the Anterior Segment of the Digestive System.

4. Structural Features of the oral mucosa.

5. Lips. Structure of Different zones.

6. Structural Features of the Cheeks.

7. Histological structure of the Gums and hard palate.

8. Structural features of the soft palate and uvula.

9. Structure of the tongue.

10. Structure of filiform papillae.

11. Fungiform papillae. Localization and structure.

12. Vallate papillae.

13. Structure of foliate papillae.

14. Taste bud: structure, Functions.

Situational Problems

1. Gastrointestinal diseases are often accompanied by a white coating on the tongue. Which tongue structures are involved in this process, and what is its mechanism?

2. Microscopic specimens show sections of the ventral, lateral, and dorsal surfaces of the tongue. What criteria can be used to distinguish them?

3. Specimens are prepared from the tip and the root of the tongue. What specific features allow them to be differentiated?

4. Specimens are prepared from the body of the tongue and the soft palate, both of which have a muscular tissue base. How can these structures be distinguished, and what is their origin?

5. A patient has damaged taste buds at the root of the tongue. Which taste sensations will be impaired?

6. If taste buds at the tip of the tongue are damaged, which taste sensations will be impaired?

Electron photomicrograph 23. Apical part of a taste bud. X 10,000:

1 — taste pore; 2 — microvilli of taste cells (taste hairs); 3 — cellular filaments in the Cytoplasm of taste cells (from Rodin's atlas)

Sample Examination Questions

1. Lips. Features of the histological structure of individual parts.

2. Cheeks. Features of the histological structure of individual parts.

3. Histological structure of the hard palate region.

4. Structure of the soft palate.

5. Filiform and fungiform papillae. Structural and functional characteristics.

6. Foliate papillae. Features of histological structure. Functional significance.

7. Circumvallate papillae. Features of histological structure. Functional significance.

8. Structure and Histology of taste buds.

9. Glands of the tongue. Features of their structure in various Regions of the tongue.

10. Histological structure of the gingiva. Epithelial attachments.