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Structure and Function of Salivary Glands Features and Functions of the Salivary Glands

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Structure and Function of Salivary Glands Features and Functions of the Salivary Glands Structure and function of Salivary Glands Features and Functions of the Salivary Glands Main functions: - Produces and secretes saliva - Cleanses the mouth - Dissolves food chemicals so they can be tasted - Moistens food, compacting it into a bolus - Begins the chemical breakdown of food • Salivary amylase: starch Types salivary glands The major salivary glands are paired glands with long ducts that empty into the oral cavity. - The parotid gland is located subcutaneously, below and in front of the ear in the space between the ramus of the mandible and the styloid process of the temporal bone. - The submandibular gland is located under the floor of the mouth, in the submandibular triangle of the neck. - The sublingual gland is located in the floor of the mouth anterior to the submandibular gland. Saliva travels to oral orifice via ducts from all three glands 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. Common properties of the salivary glands Secretory Gland Acini Secretory acini are organized into lobules. - 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. Acini are of three types: serous, mucous, or mixed. - The basic secretory unit of salivary glands, the salivon, consists of the acinus, intercalated duct, the striated duct and the excretory duct. - The acinus is a blind sac composed of secretory cells. - Three types of acini are described: . 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. Diagram comparing the components of the salivon in the three major salivary glands. The four major parts of the salivon the acinus, intercalated duct, striated duct, and excretory duct are color-coded. The three columns on the right of the salivon compare the length of the different ducts in the three salivary glands. The red-colored cells of the acinus represent serous-secreting cells, and the yellow-colored cells represent mucus-secreting cells. The ratio of serous-secreting cells to mucus-secreting cells is depicted in the acini of the various glands. Serous demilunes are artifacts of the traditional fixation method. Relationship of serous-secreting cells and mucus-secreting cells in the mixed acinus. a. This drawing indicates the relationship of the mucous and serous cells as observed in the electron microscope after the rapid freezing method. The serous cells extend from the basal lamina to the lumen of the acinus. b. In this drawing, serous cells are shown occupying the periphery of the acinus to form the so-called serous demilune. This feature is visible in routine preparations using immersion fixation. The swollen mucous cells have forced out the serous cells, leaving small remnants of the cytoplasm between the mucous cells. Types of acini in salivary glands Types of salivary glands Salivary Gland Cells - Serous cells are actually seromucous cells that produce proteins and polysaccharides - They are pyramidal and have basal spherical euchromatic nucleus - Cytoplasm is basophilic due to presence of a developed RER, Golgi apparatus - Apically located zymogen granules that are usually eosinophilic and rich in ptyalin (salivary amylase) - Many basal mitochondria - Intercellular plasmalemma processes - Organized as acinus or demilune that secrete proteins, polysaccharides and ptyalin. Electron micrograph of the apical portion of parotid gland serous cells. As indicated by the box in the orientation photomicrograph, only the apical portions of parotid gland serous acinus are shown in this electron micrograph. The cells are polarized, with their product package within the secretory vesicles (SV) near the lumen (L) of the acinus. The cells display rough endoplasmic reticulum (rER) and several profiles of the Golgi apparatus (G). Immature secretory vesicles (IV) are present close to the Golgi apparatus. At the apical pole of the cells are junctional complexes (JC). The intercellular space (IC) is dilated, and profiles of sectioned lateral plications are seen. M, mitochondria. 15,000. Salivary Gland Cells - Mucous cells are cuboidal or pyramidal - Mucous cells have a heterochromatic basal flattened nucleus - Apical cytoplasm is pale or blue/purple - Their structure is acinar or tubular - They have less RER, fewer mitochondria but greater GA Mucous acinus Low magnification electron micrograph of a mucous acinus. The mucous cells contain numerous mucinogen granules. Many of the granules have coalesced to form larger irregular masses that will ultimately discharge into the lumen (L) of the acinus. Myoepithelial cell processes (MyC) are evident at the periphery of the acinus. 5,000. Mixed salivary gland Mixed salivary gland Electron micrographs of mixed acini. a. Low magnification electron micrograph of the sublingual gland, prepared by the rapid freezing and freeze-substitution method, shows the arrangement of the cells within a single acinus. The mucous cells have well-preserved round mucinogen granules. The mucous and serous cells are aligned to surround the acinus lumen. Serous demilunes are not evident. 6,000. b. Electron micrograph of the sublingual gland prepared by traditional fixation in formaldehyde. Note the considerable expansion and coalescence of the mucinogen granules and the formation of a serous demilune. 15,000. (Courtesy of Dr. Shohei Yamashina.) Salivary Gland Cells Myoepithelial cells (Basket cells) contractile cells, they have large processes which form desmosomal contact with acini and ducts cells. - Their processes are rich in actin and myosin - Basket cells have a common basal lamina with acinar cells - They attach to basal lamina by hemidesmosome Myoepithelial cells (Basket cells) Myoepithelial cells (a) The TEM shows two salivary gland cells Containing secretory granules, with an Associated myoepithelial cell (M).X20,000. (b) A myoepithelial cell immunostained Brown with antibodies against actin show Its association with cells of acinus stained by H&E. X200. * Contraction of the myoepithelial cell compresses the acinus and aids in the expulsion of secretory products into the duct. Myoepithelial cells (Basket cells) Stellate shaped cells which embrace acini and duct as an octopus Electron micrograph of the basal portion of an acinus. This electron micrograph shows the basal portion of two secretory cells from a submandibular gland. A myoepithelial cell process is also evident. Note the location of the myoepithelial cell process on the epithelial side of the basal lamina. The cytoplasm of the myoepithelial cell contains contractile filaments and densities (arrows) similar to those seen in smooth muscle cells. The cell on the left with the small nucleus is a lymphocyte. Having migrated through the basal lamina, it is also within the epithelial compartment. Arrowheads, cell boundaries; asterisks, basolateral folds. 15,000. Introduction The primary function of the salivary glands is to moisten the mucous membranes of the upper aerodigestive tract . In humans , this function is fulfilled by the continuous exocrine secretion of numerous minor salivary glands. These glands are located in the submucosa throughout the oral cavity, pharynx, and upper airways. In developed species, most of the saliva is elaborated by three pairs of major glands, or salivary glands, named by their location: the parotid, the submaxillary or submandibular, and the sublingual glands. They are connected symmetrically to the oral cavity , where they empty their secretion only under specific stimuli. The saliva produced by these glands (750 “1000 mL/24 hours) plays an important role in preparing food for digestion , as well as in controlling the bacterial flora of the mouth. The quality of the saliva produced by the major glands is variable and depends on both the stimuli and the predominant participating gland. 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 parotid gland is located subcutaneously, below and in front of the ear in the space between the ramus of the mandible and the styloid process of the temporal bone. The submandibular gland is located under the floor of the mouth, in the submandibular triangle of the neck. 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. Each salivary gland arises from the developing oral cavity epithelium. Initially, the gland takes the form of a solid cord of cells that enters the mesenchyme. The proliferation of epithelial cells eventually produces highly branched epithelial cords with bulbous ends. Degeneration of the innermost cells of the cords and bulbous ends leads to their canalization. The cords become ducts, and the bulbous ends become secretory acini. Secretory Gland Acini - Secretory acini are organized into lobules. The major salivary glands are surrounded by a capsule of moderately
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