Department of Anatomy &Histology Digestive System

Department of Anatomy &Histology Dr.Raja Ali ---------------------------------------------------------------------- Digestive System Salivary Glands: Consist of two classes : The major salivary glands & the minor salivary glands. The major salivary glands are paired glands with long ducts that empty into the oral cavity. The major salivary glands, as noted above, consist of the paired parotid, submandibular, and sublingual glands. The parotid and the submandibular glands are actually located outside the oral cavity; their secretions reach the cavity by ducts. The sublingual gland is located in the floor of the mouth anterior to the submandibular gland. The minor salivary glands are located in the submucosa of different parts of the oral cavity. They include the lingual, labial, buccal, molar, and palatine glands. The major salivary glands are surrounded by a capsule of moderately dense connective tissue from which septa divide the secretory portions of the gland into lobes and lobules. The minor salivary glands do not have a capsule. Secretory acini are organized into lobules. Acini are of three types: serous, mucous, or mixed. Serous acini, which contain only serous cells and are generally spherical Mucous acini, which contain only mucous cells and are usually more tubular Mixed acini, which contain both serous and mucous cells. In routine H&E preparations, mucous acini have a cap of serous cells that are thought to secrete into the highly convoluted intercellular space between the mucous cells. Because of their appearance in histologic sections, such caps are called serous demilunes [Fr., half-moon]. The basic secretory unit of salivary glands, the salivon, consists of the acinus, intercalated duct, and excretory duct (Fig.1). The acinus is a blind sac composed of secretory cells. Serous cells are protein-secreting cells. Serous cells have a pyramidal shape, with a relatively wide basal surface facing the basal lamina and a small apical surface facing the lumen of the acinus. Mucous cells are mucin-secreting cells. Mucus is synthesized and stored within the cell as mucinogen granules. When the product is discharged after hormonal or neural stimulation, the cell begins to resynthesize mucus. Myoepithelial cells are contractile cells that embrace the basal aspect of the acinar secretory cells.They lie between the basal plasma membrane of the epithelial cells and the basal lamina of the epithelium . Myoepithelial cells also underlie the cells of the proximal portion of the duct system. In both locations, the myoepithelial cells are instrumental in moving secretory products toward the excretory duct. Salivary Ducts The lumen of the salivary acinus is continuous with that of a duct system that may have as many as three sequential segments: • Intercalated duct, which leads from the acinus. Intercalated ducts are located between a secretory acinus and a larger duct. Intercalated ducts are lined by low cuboidal epithelial cells • Striated duct, so-called because of the presence of “striations,” the infoldings of the basal plasma membrane of the columnar cells that form the duct. Striated ducts are lined by a simple cuboidal epithelium that gradually becomes columnar as it approaches the excretory duct. • Excretory ducts, which are the larger ducts that empty into the oral cavity. Excretory ducts travel in the interlobular and interlobar connective tissue. Excretory ducts constitute the principal ducts of each of the major glands. The epithelium of small excretory ducts is simple cuboidal. It gradually changes to pseudostratified columnar or stratified cuboidal. As the diameter of the duct increases, stratified columnar epithelium is often seen. The parotid glands The paired serous parotid glands are the largest of the major salivary glands, enter the oral cavity opposite the second upper molar tooth. The secretory units in the parotid are serous and surround numerous, long, narrow intercalated ducts. Striated ducts are large and conspicuous ((Fig. 1A).).Large amounts of adipose tissue often occur in the parotid gland; Mumps, a viral infection of the parotid gland, can damage the facial nerve. Submandibular Gland The submandibular glands are mixed glands that are mostly serous in humans. The large, paired, mixed submandibular glands are located under either side of the floor of the mouth. A duct runs forward to a papilla located on the floor of the mouth just lateral to the frenulum of the tongue. Some mucous acini capped by serous demilunes Intercalated ducts are less extensive than in the parotid gland (Fig. 1B). Sublingual Gland The small sublingual glands are mixed glands that are mostly mucous secreting in humans. are located in the floor of the mouth anterior to the submandibular glands. (Fig. 1C). Their ducts empty into the floor of the mouth. Some of the predominant mucous acini exhibit serous demilunes. Intercalated ducts and striated ducts are short, difficult to locate, or sometimes absent. Saliva Saliva includes the combined secretions of all the major and minor salivary glands. Saliva performs both protective and digestive functions: Moistening the oral mucosa. Moistening dry foods to aid swallowing. Providing a medium for dissolved and suspended food materials that chemically stimulate taste buds. Buffering the contents of the oral cavity, because of its high concentration of bicarbonate ions. Digesting carbohydrates with the digestive enzyme _-amylase. Controlling the bacterial flora of the oral cavity by use of lysozyme Saliva is a source of calcium and phosphate ions essential for normal tooth development and maintenance. Saliva performs immunologic functions, saliva contains antibodies, salivary immunoglobulin A (IgA). Fig.1:salivary glands. A-Parotid gland. B-Submandibular gland. C-Sublingiual gland. .

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