Salivary Glands PDF

Salivary Glands Regarding salivary glands, note that There are main and minor salivary glands The main salivary glands are paired and are located some distance from the oral cavity (with which they are connected by ducts); these glands include parotid, submandibular and sublingual glands T...

Salivary Glands Regarding salivary glands, note that There are main and minor salivary glands The main salivary glands are paired and are located some distance from the oral cavity (with which they are connected by ducts); these glands include parotid, submandibular and sublingual glands The minor salivary glands are located in the mucosa (and submucosa) of the tongue and in the walls of the buccal cavity. They include lingual, labial, buccal and palatal glands Saliva is the tasteless, odourless and clear fluid produced by the salivary glands. It contains digestive amylase, lysozyme, immunoglobulin A (IgA) and some ions Importance of saliva includes: Lubrication of food, to facilitate chewing and swallowing Washing of food debris from the teeth; this prevents dental caries and enhances oral hygiene Moistening of the buccal cavity; this enhances speech Creation of an appropriate environment for gustation (taste) Enhancement of immunity (owing to its contents of lysozyme and IgA) Digestion of carbohydrates (owing to its content of amylase) Main Salivary Glands (Fig. 145) These include: Parotid gland Submandibular gland, and Sublingual gland Parotid Gland (Fig. 145) The parotid gland Is the largest of the salivary glands; it resembles an inverted 3-sided pyramid Is irregular, lobulated, and yellowish in appearance Occupies the parotid region – the wedge-shaped interval between the mandibular ramus anteriorly, the mastoid process and sternocleidomastoid posteriorly, the styloid process medially and the external acoustic meatus superiorly Has a small accessory part which lies on the masseter (between the zygomatic arch above and the parotid duct below Weighs about 25 g in an average adult Is invested by a condensation of the investing layer of the deep cervical fascia – the parotid sheath. This prevents the swelling of the gland in certain pathological conditions Is separated from the submandibular gland by the stylomandibular ligament (a condensation of the deep fascia of the neck); this ligament extends from the temporal styloid process to the angle of the mandible Has several surfaces; these include superficial, superior, anteromedial and posteromedial surfaces, and an apex that is directed downwards Contains some lymph nodes – the parotid nodes; these are located in its substance and on its superficial surface  Is traversed by some structures collectively termed intraparotid structures; these include the retromandibular vein, external carotid artery and facial nerve Consists mainly of serous acini; mucous cells are scanty or absent. Thus, it Produces a watery serous fluid that is rich in enzymes; this forms about 25% of total salivary secretion Fig. 145. Salivary glands. Anatomic Relations of the Parotid Gland Regarding the relations of the parotid gland, note the following points: Its superficial surface is related to skin, superficial fascia and superficial parotid nodes Its superior surface is related to the cartilaginous part of the external acoustic meatus and the TMJ Its anteromedial surface is related to the masseter, ramus of the mandible and medial pterygoid; the terminal branches of facial nerve emerge from this surface Its posteromedial surface is related to mastoid and styloid processes, sternocleidomastoid, posterior belly of digastric, internal and external carotid arteries, internal jugular vein and the muscles attached to the styloid process (e.g. stylohyoid) Its apex is directed downwards into the carotid triangle (on the posterior belly of digastric) Intraparotid Structures Within the parotid glands, note that The facial nerve is the most superficial major structure; its five terminal branches (temporal, zygomatic, buccal, marginal mandibular and cervical) arise within the gland  The retromandibular vein descends just deep to the facial nerve (behind the ramus of the mandible); this vein is formed by the union of the maxillary and superficial temporal veins (behind the neck of the mandible) The external carotid artery is the most internal major structure; this vessel ascends through the parotid gland, deep to the retromandibular vein and facial nerve. Its terminal branches (superficial temporal and maxillary arteries), and occasionally the posterior auricular artery, arise within the gland Few (deep parotid) lymph nodes are also found The parotid duct Measures 5 cm in length (same as for submandibular duct) and 3 mm in diameter Passes forwards, over the masseter, to the anterior border of this muscle; and then turns medially, to pierce the buccal pad of fat and the buccinator muscle Terminates on a small mucosal papilla located opposite the 2nd upper molar tooth, where it opens into the vestibule of the oral cavity Is related above to the accessory parotid gland, the duct of which joins it Is lined by stratified squamous epithelium near its oral end and elsewhere by columnar epithelium Can be readily palpated over a contracted masseter Blood Supply to the Parotid Gland The parotid gland Receives branches of the external carotid artery Is drained by veins which join the retromandibular (and thus the external jugular) vein Lymph from the parotid gland drains into the following nodes: The superficial and deep parotid nodes, and The superficial and deep cervical nodes Innervation of the Parotid Gland The parotid gland receives Sympathetic fibres from the external carotid plexus, and Parasympathetic fibres from the otic ganglion (via the auriculotemporal nerve) Regarding the parasympathetic innervation of the parotid gland, note the following: Preganglionic parasympathetic fibres arise from the inferior salivatory nucleus of the upper medulla and are conveyed first by the glossopharyngeal nerve The tympanic branch of glossopharyngeal nerve contains preganglionic parasympathetic fibres; this nerve joins the tympanic plexus (located on the medial wall of the middle ear) From the tympanic plexus, the lesser petrosal nerve arises; this enters the infratemporal fossa via the foramen ovale where it ends in the otic ganglion Postganglionic parasympathetic (secretomotor) fibres from the otic ganglion are conveyed by auriculotemporal nerve to the parotid gland; these fibres enhance the secretory function of the gland Sublingual Gland The sublingual gland Is the smallest of the main salivary glands; it is shaped like an almond (Fig. 145)  Is located beneath the sublingual fold (underneath the tongue), between the mandible laterally (where it occupies the sublingual fossa) and the genioglossus medially Weighs about 3.5 g in health Is joined to its fellow around the frenulum of the tongue, close to the symphysis menti May possess up to 20 smaller sublingual ducts, which open separately on the sublingual fold; some of these ducts may unite to form a major sublingual duct which opens with the submandibular duct on the sublingual papilla Consists mainly of mucous acini with serous demilunes. Thus, its secretion is largely mucous Relations of the Sublingual Gland The sublingual gland is related Above to the mucosa of the oral floor and the tongue Below to mylohyoid Laterally to the body of the mandible (where it lies in the sublingual fossa) Medially to genioglossus, submandibular duct and lingual nerve Anteriorly to the symphysis menti and the anterior end of the opposite (sublingual) gland Behind to the deep part of the submandibular gland Blood Supply, Innervation and Lymphatics Note the following points: The sublingual gland receives branches of the sublingual and submental arteries (from the lingual and facial arteries respectively) Venous drainage of the gland is by the sublingual and submental veins Postsynaptic parasympathetic fibres to the sublingual gland arise from the submandibular ganglion, and are conveyed to the gland by the lingual nerve Submandibular Gland The submandibular gland Is an irregular gland, just about the size of a walnut (approximately half the size of the parotid gland) (Fig. 145) Consists of a large superficial part and a small deep part, the two being continuous with each other around the posterior border of mylohyoid Is mainly seromucous; it thus consists largely of serous acini with few mucous ones May contain some lymph nodes in its substance Superficial Part of Submandibular Gland The superficial part of submandibular gland Occupies the digastric (submandibular) triangle between the mandible laterally (where the gland occupies the submandibular fossa) and the mylohyoid medially Reaches as far forwards as the anterior belly of digastric, and is separated behind from the parotid gland by the stylomandibular ligament Is invested by the investing layer of deep cervical fascia; this fascial sheath is attached below to the greater horn of hyoid and above to the lower border and mylohyoid line of mandibular body Is grooved on its posterosuperior aspect by the facial artery (which later lies lateral to the gland)  Is continuous with the deep part (of submandibular gland) around the posterior border of mylohyoid Has inferior, lateral and medial surfaces The superficial part of the submandibular gland is related Medially to mylohyoid, styloglossus, hyoglossus and posterior belly of digastric; other medial relations include glossopharyngeal, lingual, hypoglossal and mylohyoid nerves, submandibular ganglion, deep lingual vein, stylohyoid ligament and the pharynx Laterally to the body of the mandible (where the gland occupies the submandibular fossa), facial artery and medial pterygoid Inferiorly to platysma, facial vein, cervical branch of facial nerve, submandibular lymph nodes and skin Deep Part of the Submandibular Gland The deep part of the submandibular gland Lies behind the sublingual gland, above the posterior part of mylohyoid Is related medially to hyoglossus and styloglossus, above to lingual nerve and below to hypoglossal nerve The submandibular duct Measures 5 cm in length (same as for the parotid duct) Begins as numerous tributaries in the superficial part of the gland Traverses the deep part (of the submandibular gland), draining it as it does so. It then Emerges from the deep part of the gland to continue forwards, medial to the sublingual gland; it crosses the lingual nerve medially as it does so Terminates at the tip of the sublingual papilla, just adjacent to lingual frenulum, on the floor of the mouth Blood Supply and Lymphatics of the Submandibular Gland The submandibular gland Receives branches of the facial and lingual arteries; the submental branch of facial artery is a notable source of blood to this organ Is drained by veins which accompany the arteries Is drained by the submandibular and deep cervical nodes (especially the jugulo-omohyoid nodes) Innervation of the Submandibular Gland Regarding the innervation of the submandibular gland, note that Postganglionic sympathetic fibres reach the gland via the nerve plexus around the facial artery Preganglionic parasympathetic fibres to the gland arise from the superior salivatory nucleus in the lower pontine tegmentum; these fibres are conveyed first by the facial nerve and then by the chorda tympani (a branch of facial nerve) In the infratemporal fossa, the chorda tympani joins the lingual nerve; via the latter, the preganglionic parasympathetic fibres of chorda tympani reach the submandibular ganglion The submandibular ganglion is located on the lateral aspect of hyoglossus, below the lingual nerve, to which it is connected by nerve fibres Fibres of the chorda tympani (contained in the sheath of the lingual nerve) synapse on the cells of the submandibular ganglion; from the latter, postganglionic parasympathetic fibres pass to the submandibular gland. Similar fibres reach the sublingual gland via the lingual nerve Applied Anatomy Note the following points: Sialography is the radiographic demonstration of the salivary glands (especially the parotid and submandibular glands); the contrast medium is injected through the main ducts of these glands. However, Owing to the multiplicity of the ducts of the sublingual gland, it is difficult to demonstrate this gland radiographically Sialogram can readily reveal calculi in the ducts of the salivary glands In carcinoma of the submandibular gland, surgical removal may be necessary; the incision is made below the angle of the mandible, to preserve the marginal mandibular branch of facial nerve