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Digestive Tract  SUMMARY OF KEY POINTS Oral Cavity

  • The oral cavity is lined primarily by mucosa with nonkeratinized stratified squamous epithelium, with keratinized stratified squamous epithelium on the hard palate and gingiva.

  • The dorsal surface mucosa of the tongue has projecting lingual papillae of four types: filiform papillae with keratinized epithelium and nonkeratinized foliate, fungiform, and large vallate papillae.

  • All lingual papillae, except the filiform type, have epithelial taste buds on their sides, with chemosensory gustatory cells with synapses to basal sensory innervation, support cells, and an apical taste pore.

  • Each tooth has enamel covering its crown and neck and a vascularized, innervated central pulp cavity within the dentin that makes up the roots and extends into the neck.

  • Enamel calcifies as parallel enamel rods in a process guided by the protein amelogenin after secretion from columnar epithelial cells called ameloblasts in the enamel organ of the embryonic tooth bud.

  • Predentin is secreted as elongated dentinal tubules from tall odontoblasts, which line the pulp cavity and persist in the fully formed tooth, with apical odontoblast processes extending between the tubules.

  • The periodontium of each tooth consists of a thin layer of bone-like cementum surrounding dentin of the roots and the periodontal ligament binding the cementum to alveolar bone on the jaw socket.

Layers of the Digestive Tract
  • From the esophagus to the rectum, the digestive tract has four major layers: a lining mucosa, a submucosa, a muscularis, and an outermost adventitia or mesothelium-covered serosa.

  • The mucosa varies regionally along the tract but always consists of a lining epithelium on a lamina propria of loose connective tissue and smooth muscle fibers extending from muscularis mucosae layer.

  • The mucosa of the esophagus has nonkeratinized stratified squamous epithelium; its muscularis is striated at its superior end with smooth muscle at its inferior end, with mixed fiber types in the middle.

  • Most of the outer layer of the esophagus is adventitia, merging with other tissues of the mediastinum.

  • At the esophagogastric junction, stratified squamous epithelium changes abruptly to simple columnar epithelium invaginating into the lamina propria as many branched tubular glands.

  • The stomach has four major regions: the superior cardia and inferior pylorus, which are rather similar histologically, and the intervening fundus and body, which are also similar.

  • The mucosa of the stomach fundus and body is penetrated by numerous gastric pits, which are lined like the stomach lumen with surface mucous cells and which lead into branching gastric glands.

  • The surface mucous cells secrete a thick layer of viscous mucus with bicarbonate ions, which protects these cells and the underlying lamina propria.

  • The gastric glands are lined by epithelium with four major cell types, as well as their pluripotent stem cells that are located in the narrow neck regions of these glands:

    • Mucous neck cells include ...

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