Salivary glands

Complete anatomy and physiology of salivary glands

1. Salivary Glands Chairman: Dr. A. P. Bellad Co- Chairman: Dr. P. S. Pattanshetti Presenter: Dr. S S K Kanth Kavipurapu

2. Scheme of Presentation Introduction Anatomy Parotid gland Sub-Mandibular gland Sub lingual glands Minor salivary glands Physiology

3. Introduction Salivary glands are compound, tubuloacinar exocrine glands whose ducts open into the oral cavity. They secrete saliva, a fluid which lubricates food to assist deglutition, moistens the buccal mucosa, which is important for speech, and provides an aqueous solvent necessary for taste and a fluid seal for sucking and suckling.

4. Introduction They also secrete digestive enzymes, e.g. salivary amylase, and antimicrobial agents, e.g. immunoglobulin A (IgA), lysozyme and lactoferrin , into saliva. The major salivary glands are the P arotid , S ubmandibular and S ublingual glands. In addition, there are numerous minor salivary glands scattered throughout the oral mucosa and submucosa .

5. Introduction Approximately 0.5 L of saliva is secreted per day. Salivary flow rates are typically 0.3 mL/min when unstimulated, and rise to 1.5–2 mL/min when stimulated. Flow rate is negligible during sleep. In the unstimulated state, the parotid gland contributes 20%, the submandibular gland 65%, and the sublingual and minor salivary glands 15 % When stimulated, the parotid contribution rises to 50 %.

6. Parotid Gland The paired parotid glands are the largest of the salivary glands. Each has an average weight of 25 g It is irregular , lobulated, yellowish mass, lying largely below the external acoustic meatus between the mandible and sternocleidomastoid The gland also projects forwards onto the surface of masseter.

7. Parotid Gland In 20% of cases, a small, usually detached, part called the accessory parotid gland (pars accessoria or socia parotidis ) lies between the zygomatic arch above and the parotid duct below .

8. Parotid Capsule The investing layer of the deep cervical fascia forms a capsule for the gland. The Fascia splits to enclose the gland The superficial lamina – thick and adherent to the gland T he deep lamina is thin and is attached to the styloid process, the mandible and the tympanic plate.

9. External features The gland resembles a three sided pyramid. The apex of the pyramid directed downwards. The gland has four surfaces Superior Superficial Anteromedial Posteromedial

10. External Features The surfaces are separated by three borders. Anterior Posterior Medial

11. Relations

12. R elations The concave superior surface cartilaginous part of the external acoustic meatus posterior aspect of the temporomandibular joint. auriculotemporal nerve The apex overlaps the posterior belly of digastric and the carotid triangle to a variable extent. The cervical branch of the facial nerve Two divisions of the retromandibular vein

13. Relations The superficial surface skin and superficial fascia, containing the facial branches of the great auricular nerve, superficial parotid lymph nodes and the posterior border of platysma . The parotid fascia

14. Relations The anteromedial surface is grooved by the posterior border of the mandibular ramus. Masseter , The lateral aspect of the temporomandibular joint Posterior border of the mandibular ramus. Medial pterygoid . Emerging branches of the facial nerve

15. Relations The posteromedial surface Mastoid process, Sternocleidomastoid , Posterior belly of the digastric, and The styloid process The external carotid artery grooves this surface before entering the gland , The internal carotid artery lies deep to the styloid process

16. Borders Anterior – Separates superficial surface from anteromedial surface Structures emerging – Parotid duct Terminal branches of the facial nerve Transverse facial vessels

17. Borders Posterior – separates superficial surface from the posteromedial surface. It overlaps the sternocleidomastoid Medial – separates the anteromedial from posteromedial. It is related to the lateral wall of pharynx.

18. Structures within the gland Arteries The external carotid artery (enters through posteromedial surface) divides into maxillary artery (anteromedial surface). the superficial temporal artery emerge from anterior part of superficial surface. The posterior auricular artery may also branch from the external carotid artery within the gland, leaving by its posteromedial surface.

19. Structures within the gland

20. Structures within the gland Veins The retromandibular vein, formed by the union of the maxillary and superficial temporal veins. The vein divides into anterior and posterior divisions Nerves The facial nerve – enters through the upper part of the posteromedial surface and divides into terminal branches and leaves through the anteromedial surface. Parotid lymph nodes.

21. Parotid Duct The average dimensions of the parotid duct are 5 cm long and 3 mm wide. the duct appears at the anterior border of the upper part of the gland and passes horizontally across masseter, between the angle of the mouth and the zygomatic arch It crosses masseter, and traverses the buccal fat pad and buccinator opposite the crown of the upper third molar tooth.

22. Parotid duct

23. Parotid Duct The duct then runs obliquely forwards between buccinator and the oral mucosa and opens upon a small papilla opposite the second upper molar crown. The submucosal passage of the duct serves as a valvular mechanism preventing inflation of the gland with raised intraoral pressures. While crossing masseter, the duct lies between the upper and lower buccal branches of the facial nerve, and may receive the accessory parotid duct.

24. Vascular supply and Lymphatic drainage T he external carotid artery and its branches within and near the gland supply the parotid. The veins drain to the external jugular vein via local tributaries . Lymph drains first into the parotid nodes and from there to the upper deep cervial nodes.

25. Innervation Preganglionic nerves travel in the lesser petrosal branch of the glossopharyngeal nerve and synapse in the otic ganglion. Postganglionic secretomotor fibres reach the gland via the auriculotemporal nerve

26. Submandibular Gland The submandibular gland is roughly ‘J’ shaped and about the size of a walnut. It is indented by the posterior border of the mylohyoid which divides it larger superficial smaller deep part , It is a seromucous (but predominantly serous) gland.

27. Submandibular Gland The gland is partially enclosed between two layers of the deep cervical fascia. The superficial layer of the fascia covers the inferior surface of the gland and is attached to the base of the mandible T he deep layer covers the medial surface of the gland and is attached to the mylohyoid line of the mandible.

28. Submandibular Gland

29. Superficial Part The superficial part of the gland is situated in the digastric triangle where it reaches forward to the anterior belly of digastric and back to the stylomandibular ligament, by which it is separated from the parotid gland It has 3 surfaces Inferior Lateral Medial

30. Relations Inferior surface Skin Platysma C ervical branch of the facial nerve D eep fascia F acial vein S ubmandibular lymph nodes

31. Relations Lateral surface S ubmandibular fossa on the mandible I nsertion of the medial pterygoid F acial artery Medial surface – divided into 3 parts Anterior M iddle P osterior

32. Relations Anterior M ylohyoid muscle, nerve and vessels Middle Hyoglossus S tyloglossus L ingual nerve T he submandibular ganglion H ypoglossal nerve

33. Relations Posterior Styloglossus T he stylohoid ligament T he ninth nerve W all of the pharynx It overlaps the stylohyoid and the posterior belly of the digastric

34. Deep part The deep part of the gland extends forwards to the posterior end of the sublingual gland. It lies deep to Mylohyoid , superficial to Hyoglossus and styloglossus medially, It is continuous with the superficial part around the posterior border of Mylohyoid .

35. Submandibular Duct It is thin walled and is 5 cm long Emerges from the anterior end of the deep part of the glands and runs forwards on the hypoglossus between the lingual and hypoglossal nerve. At the anterior border of the hypoglossus the duct is crossed by the lingual nerve. It opens on the floor of the mouth, on the summit of the sublingual papilla, at the side of the frenulum of the tongue.

36. Blood supply and Innervation Facial artery supplies the gland. V ein drains into the common facial or lingual vein Lymph passes to submandibular lymph nodes. Supplied by branches of the submandibular ganglion Secretomotor fibers S ensory fibres from the lingual nerve V asomotor sympathetic fibres from the plexus on the facial artery.

37. Sublingual Gland The sublingual gland is the smallest of the main salivary glands. E ach gland is narrow, flat, shaped like an almond, and weighs approximately 4 g. The sublingual gland lies on mylohyoid , and is covered by the mucosa of the floor of the mouth, which is raised as a sublingual fold.

38. Sublingual Gland The anterior end of the contralateral sublingual gland lies in front, and the deep part of the submandibular gland lies behind The mandible above the anterior part of the mylohyoid line, the sublingual fossa, is lateral, and genioglossus is medial, separated from the gland by the lingual nerve and submandibular duct. The sublingual glands are seromucous , but predominantly mucous .

39. Blood supply and innervation The arterial supply is from the sublingual branch of the lingual artery the submental branch of the facial artery. Innervation is via the submandibular ganglion. Lymphatic drainage is to the submental nodes.

40. Sublingual ducts About 15 ducts emerge form the gland They open directly into the floor of the mouth on the summit of the sublingual fold. Few of them join the submandibular duct.

41. Minor salivary glands Labial Buccal Palatoglossal , Palatal Lingual glands

42. Physiology In the salivary glands, the secretory (zymogen) granules containing the salivary enzymes are discharged from the acinar cells into the ducts. The pH of saliva from resting glands is slightly less than 7.0, but during active secretion, it approaches 8.0. Saliva contains two digestive enzymes: lingual lipase, secreted by glands on the tongue, and salivary α -amylase, secreted by the salivary glands.

43. Characteristics

44. Physiology Saliva also contains mucins , glycoproteins that lubricate the food, bind bacteria, and protect the oral mucosa. It also contains the secretory immune globulin IgA, lysozyme , which attacks the walls of bacteria; lactoferrin , which binds iron and is bacteriostatic; and proline -rich proteins that protect tooth enamel and bind toxic tannins. .

45. Physiology Saliva performs a number of important functions. It facilitates swallowing, keeps the mouth moist, serves as a solvent for the molecules that stimulate the taste buds, aids speech by facilitating movements of the lips and tongue, and keeps the mouth and teeth clean.

46. Physiology The saliva also has some antibacterial action The buffers in saliva help maintain the oral pH at about 7.0. They also help neutralize gastric acid and relieve heartburn when gastric juice is regurgitated into the esophagus

47. Ionic Composition of Saliva There is considerable variation in the ionic composition of saliva from species to species and from gland to gland . In general, however, saliva secreted in the acini is probably isotonic, with concentrations of Na + , K + , Cl - , and HCO 3 - that are close to those in plasma . The excretory ducts and probably the intercalated ducts that drain into them modify the composition of the saliva by extracting Na + and Cl - and adding K + and HCO 3 - .

48. Ionic Composition of Saliva The ducts are relatively impermeable to water. Therefore , at low salivary flows, the saliva that reaches the mouth is hypotonic, slightly acidic, and rich in K + but relatively depleted of Na + and Cl - . When salivary flow is rapid, there is less time for ionic composition to change in the ducts.

49. Control of Salivary secretion Salivary secretion is under neural control Stimulation of the parasympathetic nerve supply causes profuse secretion of watery saliva with a relatively low content of organic material . Associated with this secretion is a pronounced vasodilation in the gland, which appears to be due to the local release of VIP. This polypeptide is a cotransmitter with acetylcholine in some of the postganglionic parasympathetic neurons.

50. Atropine and other cholinergic blocking agents reduce salivary secretion. Stimulation of the sympathetic nerve supply causes vasoconstriction. Food in the mouth causes reflex secretion of saliva, and so does stimulation of the vagal afferent fibers at the gastric end of the esophagus . In humans, the sight, smell, and even thought of food causes salivary secretion ("makes the mouth water").

51. Thank you