Histology Mentor

Oral histology - Questions 73-79

73. Question - Diagram the histology of the lip.

The lip consists of thin skin on the outside, oral mucosa on the inside supported by skeletal muscle. The vermilion border (red part) forms the transition from the epidermis (stratified squamous keratinized epithelium) on the outside with the non-keratinized stratified squamous epithelium of the oral mucosa on the inside.

74. Question - Describe regional variations in the oral mucosa and submucosa. Explain the role of minor salivary glands.

A mucosa consists of epithelium and a supporting connective tissue called the lamina propria. In the oral cavity and continuing through the esophagus the epithelium is stratified squamous non-keratinized except where the mucosa is tightly adherent to underlying bone (the masticatory mucosa). In those locations, the gingiva and the central region of the hard palate, parakeratin or keratin may be found and there is no submucosa. The lamina propria is a denser irregular connective tissue than the connective tissue of the submucosa where fat and minor (mostly mucous) salivary glands are found. The submucosa is most evident in the lip, soft palate and the lateral parts of the hard palate and pharynx. In the central part of the pharynx the mucosa is tightly adherent to the underlying sheet of elastic tissue and skeletal muscle. To keep the buccal mucosa from being bitten slips of skeletal muscle extend through the submucosa to attach to the lamina propria. Unlike the major salivary glands the minor salivary glands secrete continuously and their secretions contain a higher concentration of secretory immunoglobulin A.

75. Question - Diagram the histology of the soft palate. What is metaplasia?

The soft palate is supported by skeletal muscle and has oral mucosa on the underside with respiratory mucosa on the upper side. The epithelium associated with respiratory mucosa is pseudostratified ciliated columnar with goblet cells. All cilia in the respiratory tract sweep toward the oropharynx where the mucus can be swallowed. With chronic irritation the pseudostratified columnar epithelium is subject to changing to a stratified epithelium. This is called metaplasia.

76. Question - Describe the histology of the tongue. Illustrate the structure and distribution of filiform, fungiform and circumvalate papillae.

The tongue is supported by bundles of skeletal muscle oriented in three directions, front to back, side to side and top to bottom. The mucosa on the underside is thin and some drugs can be absorbed through it. Several specializations occur on its dorsal surface. Filiform and fungiform papillae are found on its anterior two thirds and lingual tonsils on its posterior one third with the circumvalate papillae between.

77. Question - Compare and contrast the histology of the parotid, submandibular and sublingual salivary glands. What are striated ducts? Illustrate their cytology.

The major salivary glands are classified as compound tubuloalveolar glands because they have a branched duct system (compound) and because they have both tubular (mucus-secreting) and acinar (serous secreting) secretory units. The branched duct system gives rise to lobules so that there are both intra- and interlobular ducts. In all the glands small, intercalated (intralobular) ducts connect the secretory units to the larger striated ducts that connect to the interlobular ducts. The striated ducts actively remove sodium from the secretions replacing only some of it with potasium with the result that the saliva is hypotonic. They are longest and thus most noticeable in the submandibular gland and the shortest in the sublingual glands. There are very few, if any, mucous tubules in the parotid gland but they predominate in the sublingual glands.

78. Question - Diagram the structure of a mature tooth.

79. Question - Diagram the structure of a developing tooth at the appositional stage. Explain the interactions of the dental organ and the dental papilla that lead to the differentiation of odontoblasts and ameloblasts.

At the stage illustrated here enamel matrix has just begun to be formed by the ameloblasts. Odontoblasts began first to make dentin and this induced the ameloblasts to complete their differentiation and start producing enamel matrix. The ameloblasts develop from the inner layer of an epithelial structure called the dental or enamel organ that caps over the dental papilla. The dental organ induces the mesenchymal cells of the dental papilla to become odontoblasts and these in turn produce dentin that induces the final differentiation of the ameloblasts.

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