Digestive System 2 PDF - Notes

Digestive system 2 Salivary glands Exocrine glands in the mouth produce saliva, which has digestive, lubricating, and protective functions. Minor salivary glands Major salivary glands: Parotid gland Submandibular gland Sublingual gland Structure of major salivary glands The major salivary gland cons...

Digestive system 2 Salivary glands Exocrine glands in the mouth produce saliva, which has digestive, lubricating, and protective functions. Minor salivary glands Major salivary glands: Parotid gland Submandibular gland Sublingual gland Structure of major salivary glands The major salivary gland consists of Secretory portion (units) Duct portion Secretory portion (units are formed from cells that secret saliva There are 3 types of secretory units (acini) : Serous, mucous and mixed (mucoserous) Secretory units 1-Serous acini: Have pyramidal cells with round nuclei and cytoplasm that are highly stained owing to the presence of many secretory vesicles containing serous proteins. 2. Mucous acini: Composed of columnar cells with flattened, basally located nuclei and lightly stained cytoplasm owing to the presence of mucous proteins within secretory vesicles that fail to stain well with common histologic stains. 3. Mixed acini (seromucous): Composed of mucous cells capped by a few serous cells as serous demilunes. Serous demilune Compare between serous acini and mucous acini Serous Have pyramidal cells Mucous acini Columnar cells Cytoplasm is highly stained lightly stained cytoplasm owing to the presence of mucous proteins Round nuclei Flattened, basally located nuclei Ducts of salivary glands Intercalated ducts: Lined by simple cuboidal epithelium Striated ducts: Lined by simple columnar epithelium Have thin longitudinal lines (striations) that are visible in light micrographs of the cytoplasm of duct cells interlobular ducts: Possessing a stratified cuboidal or stratified columnar epithelium General structure of the digestive tract The entire gastrointestinal tract has certain common structural characteristics. It is a hollow tube with a lumen of variable diameter and a wall made up of four main layers: the mucosa, submucosa, muscularis, and serosa. Mucosa, composed of Lining epithelium, Loose cellular connective tissue housing glands, known as the lamina propria, The muscularis mucosae is the outer muscular layer of the mucosa. Submucosa, Contains a dense connective tissue Houses glands, but only in the esophagus and the duodenum. Muscularis externa: Composed of smooth muscle cells organized as two or more layers. In the inner layer (closer to the lumen), the fiber orientation is generally circular; in the external layer it is longitudinal Adventitia/Serosa Innervation of the alimentary canal is accomplished by the enteric nervous system (whose neurons are located in Meissner [submucosal] and Auerbach [myenteric] plexuses. Esophagus A muscular tube Transports swallowed material from the pharynx to the stomach The esophageal mucosa has non-keratinized stratified squamous epithelial lining The submucosa contains small mucus-secreting glands, the esophageal glands, which lubricate and protect the mucosa Muscularis externa: Composed of inner circular and outer longitudinal layers of muscle fibers In the upper third, bundles of skeletal muscle predominate In the middle third, has combination of striated and smooth muscle fibers The lower third consists entirely of smooth muscle Adventitia: loose C.T. Serosa covers short segment below the diaphragm Thank you