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

Digestive System
Anterior Segment of the Digestive System
Tonsils

At the border between the Oral Cavity and the Pharynx, within the folds of the mucous membrane, lie large accumulations of lymphoid tissue. Together, they form the Pirogov–Waldeyer lymphoepithelial pharyngeal ring, which surrounds the entrance to the respiratory and digestive tracts. The largest accumulations of lymphoid tissue in this ring are called tonsils.

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Fig. 43. Section of the sublingual gland. Hematoxylin and eosin staining. x 400:

1 — loose Fibrous Connective Tissue; 2 — mucous secretory unit; 3 — seromucous (mixed) secretory unit (a — mucous Cells; b — serous cells (demilunes)); 4 — striated duct; 5 — interlobular duct

Tonsils (tonsillae) are accumulations of lymphoid tissue located within the folds of the mucous membrane.

Depending on their Location, they are classified into palatine, pharyngeal, lingual, tubal, and laryngeal tonsils.

Palatine tonsils (tonsillae palatinae). Each tonsil consists of several folds of the mucous membrane, in the lamina propria of which numerous lymphoid follicles are situated. From The surface of the tonsil, 10–20 crypts (cryptae tonsillares) extend deep into the organ, branching to form secondary crypts.

The epithelium covering the surface of the entire tonsil and its crypts is stratified squamous non-keratinized and may be infiltrated by lymphocytes and leukocytes.

The lamina propria of the mucous membrane forms papillae that grow into the epithelium. Lymphoid follicles (folliculi lymphatici) with light (reactive) centers are located in the loose fibrous connective tissue of this layer. They are formed mainly by B-lymphocytes and plasmacytes. T-lymphocytes are located in the interfollicular spaces of the tonsils.

The pharyngeal tonsil (tonsilla pharyngea) is an accumulation of lymphoid tissue in the region of the dorsal wall of the pharynx, lying between the openings of the auditory tubes. In adults, it is lined with stratified squamous epithelium; however, areas of ciliated epithelium are occasionally found within the crypts.

In the loose irregular connective tissue that forms the lamina propria of the mucous membrane, there are lymphoid follicles similar to those found in the palatine tonsil. In young children, the lymphoid tissue of the pharyngeal tonsil reaches its maximum development. Its pathological enlargement is known as adenoids.

The lingual tonsil (tonsilla lingualis) is located in the mucous membrane of the ROOT of the Tongue. The excretory ducts of the Salivary Glands of the tongue open at the bottom of its crypts, and their secretion flushes the crypts.

The tubal tonsils are located around the openings of the auditory tubes and protect the tympanic cavity from the penetration of pathogens.

Slide 8. Section of the palatine tonsil (Fig. 44).

Low magnification. Examine and draw the specimen. At this magnification, study the General structural plan of the tonsil, which consists of folds of the mucous membrane with lymphoid follicles located in its lamina propria. Note that the stratified squamous non-keratinized epithelium of the tonsils is infiltrated with lymphocytes in some areas. In these epithelial regions, alongside the nuclei of epithelial cells, numerous small, flattened lymphocyte nuclei are visible. Externally, the tonsil is covered by a capsule.

Label the following on the drawing: 1) mucous membrane: a) stratified squamous epithelium; b) lamina propria of the mucous membrane; c) palatine salivary glands (mucous); 2) tonsillar crypt; 3) lymphoid follicles; 4) infiltration of the crypt epithelium by lymphocytes; 5) migration of lymphocytes onto the epithelial surface.

Fig. 44. Section of the palatine tonsil. Hematoxylin and eosin staining. x 140:

1 — mucous membrane (a — stratified squamous epithelium; b — lamina propria of the mucous membrane; c — palatine salivary glands (mucous)); 2 — tonsillar crypt; 3 — lymphoid follicles; 4 — infiltration of the crypt epithelium by lymphocytes; 5 — migration of lymphocytes onto the epithelial surface

Review Questions

1. General characteristics of the salivary glands.

2. Cytology/practical/97.html">Parotid salivary gland. Structure and histophysiology of the secretory units.

3. Structural Features of the excretory ducts of the parotid salivary gland.

4. Submandibular salivary gland. Its structure.

5. Sublingual salivary gland. Features of its structure.

6. Pirogov-Waldeyer lymphatic ring (tonsillar ring). General characteristics.

7. Palatine tonsils, their structure.

8. Pharyngeal tonsil, its structure.

9. STRUCTURE OF THE lingual tonsil.

Electron micrograph 24. Basal part of a serous Cell from the human submandibular gland. x 30,000:

1 — Cell Nucleus; 2 — nuclear pores; 3 — Endoplasmic reticulum; 4 — Mitochondria; 5 — folds of the basal Plasmalemma; 6 — basal lamina

Electron micrograph 25. Intercellular secretory canaliculus of the terminal portion in the human submandibular gland. x 73,000:

1 — cell boundaries; 2 — junctional complexes; 3 — intercellular secretory canaliculus with cross-sectioned cellular microvilli; 4 — cellular microvilli (after Tendler)

Situational problems

1. Actinomycin D was used to block the protein-synthesizing System of the salivary glands. Which component will be missing in the saliva? How will this affect Digestion? Which cells will stop secreting their product?

2. Preparations made from the salivary glands (parotid, sublingual, and submandibular) are stained with mucicarmine, which stains mucocytes. On The basis of what features can these glands be differentiated?

3. Three micropreparations of salivary glands are provided. One shows well-developed striated ducts and intercalated ducts; all terminal portions consist of basophilic cells with granular Cytoplasm and round nuclei. In the second preparation, striated and intercalated ducts are less developed; most portions resemble those in the previous slide, but some terminal portions consist of clear cells with flattened nuclei and basophilic cells with granular cytoplasm and round nuclei, with the basophilic cells arranged as demilunes. The third preparation appears pale (clear) under low magnification because most cells of its terminal portions are clear with flattened nuclei; some terminal portions are formed exclusively by such cells, while others also contain basophilic cells with granular cytoplasm and round nuclei; intercalated ducts are absent, and striated ducts are poorly developed. Which glands are represented in the preparations?

4. The preparation of a palatine tonsil shows heavy lymphocyte infiltration of the epithelium, and the crypts contain numerous destroyed cells. What is the functional state of the tonsil?

Sample examination questions

1. Parotid salivary gland. Structure and histophysiology of secretory portions.

2. Structural features and histophysiology of the parotid gland excretory ducts.

3. Submandibular salivary gland. Structural features of secretory portions and excretory ducts.

4. Sublingual salivary gland. Structural features of secretory portions and excretory ducts.