EMBRYOLOGY , ANATOMY AND PHYSIOLOGY
The salivary glands can be divided into two ,groups: the minor and major glands. All salivary glands develop from . the embryonic oral cavity .as buds of epithelium that extend into the underlying mesenchymal tissues. The
epithelial ingrowths branch to form a primitive ductal system that eventually becomes canalized to provide f?r drainage of salivary secretions. The minor salivary J::land~ begin to develop around the fortieth day in utero, WhCTt’-
. as-the larger ma or glands begin to deve-lop sli/-:htly earher, at about the thirty-fifth day in utero, At around the seventh or eighth Elonth in utero, secretory cells called
acini begin to develop around the ductal system. The acinar cells of the salivary glands are classified as either serous’ cetls, which produce .a thin, watery serous secretion, or /IlUCOUS cells, which produce a thicker, viscous mucous secretion. The minor salivary glands are well
‘developed and functional in the newborn infant. The acini of the’ minor salivary glands primarily produce mucous secretions, although some are made ‘up of serous cells, as well. Tile major salivary glands are paired structures and are the parotid, submandibular, and sublingual glands. The parotid glands contain primarily serous acini .’ with few mucous cells. Conversely, the sublingual glands (Ire for the most part composed of mucous cel1s. The submandibular glands are mixed glands, made up of approximately equal numbers of serous and ‘mucous acini.
Between 800 and 1000 minor salivary glands are found throughout the portions of the oral cavity that are covered by mucous membranes, with a few exceptions” such as the anterior third of the hard palate, the attached gingiva, and the dorsal surface of the anterior third of the
tongue. The minor salivary glands are referred to as the labial, buccal, palatine, tonsillar (Weber’s glands), retromolor (Carrnalt’s glands), and lingual glands, which are divided into three groups: (1) inferior apical (glands of Blandin Nuhn), (2) taste buds (Ebner’s glands), and (3) posterior
lubricating glands Table 20-1).
Occasionally.’ a normal anatomic varlation occursIn which an accessory parotid duct may aid Stenson’s duct. in drainage of salivary secretions. Additionally, an acccssory portion of the parotid gland may be present somewhere along the course of Stenseri’s duct. The duct runs anteriorly from the gland and is superficial to the masseter muscle. At the location of the anterior edge of the masseter muscle, Stensen’s duct turns sharply medial and passes through the fibers of the buccinator muscle. The
duct opens into the oral cavity through the buccal mucosa, usually adjacent to the maxillary first or second molar tooth. The parotid gland receives. innervation from the ninth crania l (glossopharyngeal) nerve via the auriculotemporal nerve from the otic ganglion.
in’ rise (I the major duct of the submandibular gland .nov.n J W/lllrt()/I’~ duct. This duct passes forward along h uperior surface of the, mylohyoid muscle in the subngual space, adjacent to the lingual nerve. The anatomic
relationship is such that the lingual nerve loops under ‘harton’s duct, from lateral to medial, in the .posterior floor of the mouth. wharton’s duct is about 5 cm in I ngth, and the diameter of its lumen is 2 to 4 mm.
Wharton’s duct opens into the floor of the mouth via a punctum located close to the incisors at the most anterior aspe~t of the junction of the lingual frenum and the floor of the mouth. The punctum is’ a constricted portion of the duct, and it functions to limit retrograde flow of
bacteria laden DIal fluids. This particularly limits those bacteria that tend to colonize around the ductal orifices.
The functions of saliva are to provide lubrication for speech and mastication, to produce enzymes for digestion, and to produce compounds with antibacterial properties’ (Table 20-2). The salivary glands produce
approxitnately 1000 to 1500 ml of saliva per clay, with the highest flow rates occurring during meals. The relative contributions of each salivary gland to total daily production varies, with the submandibular gland providing 70%, the parotid gland 25%, the sublingual gland 3% to
4%, anu th minor salivary. glands contributing only trace amou ts of saliva (Box 20-1). The electrolyte composition of saliva also varies between salivary glands.
correspond to the percentage of Illl.iCOUS· and serous cells therefore the highest viscosity is in the sublingual gland, followed by the submandibular gland, and, lastly, the parotid gland,which is composed mainly of- serous cells. Interestingly, the .daily production of saliva begms to . de.crease gradually after the age of 20.