ANATOMY AND PHYSIOLOGY OF SALIVARY GLANDS.pptx

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1. ANATOMY AND PHYSIOLOGY OF SALIVARY GLANDS DR MESHWA OZA ENT RESIDENT

2. INTRODUCTION There are 3 pairs of large salivary glands, namely, P arotid gland S ubmandibular ( submaxillary) gland S ublingual gland S everal minor salivary glands are situated in the tongue, palate, cheek and lips.

3. ACINI The parotid glands are purely serous glands which secrete watery saliva containing more than 90% water. Parotid glands secrete 25% of the total salivary secretion (which is about 1500 mL/day ). The submandibular gland is composed of a mixture of serous and mucous acini, the former predominating. The sublingual gland contains both serous and mucous acini, the latter predominating. Serous gland Mucous gland Seromucous gland

4. DEVELOPMENT All major and minor salivary glands develop as sophisticated diverticula originating from the buccal epithelium. There is proliferation and budding of the epithelium as a solid cord into the mesenchyme. This later canalises and branches repeatedly to form the duct system. The terminal parts of this duct system develop into secretory acini.

5. DEVELOPMENT- PAROTID GLAND The parotid gland appears between 4 and 6 weeks of IUL . The outgrowth for the parotid gland arises in relation to the line along which the maxillary and mandibular processes fuse to form the cheek. This outgrowth gradually engulfs mesenchymal structures like the facial nerve and few lymph follicles; therefore, this gland is considered to be ectodermal .

6. The submandibular gland arises in the 6th week and sublingual gland in the 8th week . These are usually considered to be of endodermal in origin.

7. PAROTID GLAND

8. GROSS ANATOMY The parotid is the largest of the salivary glands deriving its name from para meaning 'around ‘ and otic meaning 'ear’. A bilobed structure shaped like an asymmetric dumb bell with a superficial lobe and smaller deep lobe . It weighs about 15-25 grams. It is situated below the external acoustic meatus, between the ramus of the mandible and the sternocleidomastoid . Anteriorly, the gland also overlaps the masseter muscle.

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10. CAPSULE The capsule is formed by the investing layer of the deep cervical fascia. The fascia splits to enclose the gland. The superficial lamina is inelastic, thick and adherent to the gland . Any swelling of the gland as in parotitis can be very painful, particularly when the patient opens his mouth. The hinge action occurring when the mandible is depressed compresses the swollen parotid against the mastoid process and the walls of its inelastic capsule resulting in painful mastication . The inelastic nature of the fascia also accounts for longer period of time before parotid swellings become significantly obvious.

11. The deep lamina is thin and is attached to the styloid process, mandible and tympanic plate. A portion of the deep lamina condenses into a tough unyielding band between the styloid process and the angle of the mandible called the stylomandibular ligament . The partial absence of a definite fascial barrier on the deep aspect of the gland means that parotid suppuration may spread to the parapharyngeal space. P resence of the tough stylomandibular ligament acts as a definite barrier to medial extension of tumours located in the outer part of the gland, whereas a tumour passing through the stylomandibular tunnel (between the ligament and mandible) may acquire a dumb-bell shape.

12. EXTERNAL FEATURES The gland resembles a three-sided pyramid. The apex of the pyramid is directed downwards. The gland has four surfaces: a . Superior (base of the pyramid) b . Superficial c. Anteromedial d . Posteromedial The surfaces are separated by three borders: a . Anterior b . Posterior c . Medial/pharyngeal edge

13. RELATIONS

14. THE APEX The apex overlaps the posterior belly of the digastric and the adjoining part of the carotid triangle . The cervical branch of the facial nerve and the two divisions of the retromandibular vein emerge near the apex .

15. SURFACES The superior surface or base forms the upper end of the gland which is small and concave. It is related to: a . The cartilaginous part of the external acoustic meatus. b . The posterior surface of the temporomandibular joint c . The superficial temporal vessels. d . The auriculotemporal nerve

16. The superficial surface is the largest of the four surfaces. It is covered with: a . Skin b . Superficial fascia containing the anterior branches of the greater auricular nerve, the preauricular or superficial parotid lymph nodes and the posterior fibres of the platysma and risorius . c . The parotid fascia which is thick and adherent to the gland. d . A few deep parotid lymph nodes embedded in the gland.

17. The anteromedial surface is grooved by the posterior border of the ramus of the mandible. It is related to: a . The masseter b . The lateral surface of the temporomandibular joint c . The posterior border of the ramus of the mandible d . The medial pterygoid e . The emerging branches of the facial nerve.

18. The posteromedial surface is moulded to the mastoid and the styloid processes and the structures attached to them. Thus , it is related to: a . The mastoid process , with the sternocleidomastoid and the posterior belly of the digastric. b . The styloid process , with structures attached to it. c . The external carotid artery and facial nerve enter the gland through this surface. The internal carotid artery lies deep to the styloid process.

19. BORDERS The anterior border separates the superficial surface from the anteromedial surface. It extends from the anterior part of the superior surface to the apex. The following structures emerge at this border. a . The parotid duct b . Most of the terminal branches of the facial nerve c . The transverse facial vessels. In addition, the accessory parotid gland lies on the parotid duct close to this border

20. The posterior border separates the superficial surface from the posteromedial surface . It overlaps the sternocleidomastoid. The medial edge or pharyngeal border separates the anteromedial surface from the posteromedial surface. It is related to the lateral wall of the pharynx

21. Structures within the Parotid Gland From medial to lateral side, these are as follows. Arteries : The external carotid artery enters the gland through its posteromedial surface. The maxillary artery leaves the gland through its anteromedial surface. The superficial temporal artery gives transverse facial artery and emerges at the anterior part of the superior surface.

22. Veins : The retromandibular vein is formed within the gland by the union of the superficial temporal and maxillary veins . In the lower part of the gland, the vein divides into anterior and posterior divisions which emerge close to the apex (lower pole) of the gland.

23. FACIAL NERVE In its extracranial course, the facial nerve crosses the lateral side of the base of the styloid process. Then the nerve enters the posteromedial surface of the parotid gland, runs forwards through the gland crossing the retromandibular vein and the external carotid artery. Behind the neck of the mandible, it divides into two branches— temporofacial and cervicofacial . Temporofacial gives temporal and zygomatic branches. Cervicofacial gives buccal, marginal mandibular and cervical branches. These five terminal branches emerge along the anterior border and apex of the parotid gland

24. Terminal branches i . Temporal branches cross the zygomatic arch and supply: a . Auricularis anterior b . Auricularis superior c . Intrinsic muscles on the lateral side of the ear d . Frontalis e . Orbicularis oculi (orbital, lacrimal, palpabral ) f . Corrugator supercilii . ii . The zygomatic branches run across the zygomatic bone and supply the orbicularis oculi.

25. iii. The buccal branches are two in number. The upper buccal branch runs above the parotid duct and the lower buccal branch below the duct. They supply muscles in that vicinity especially the buccinator . iv. The marginal mandibular branch runs below the angle of the mandible deep to the platysma . It crosses the body of the mandible and supplies muscles of the lower lip and chin . v. The cervical branch emerges from the apex of the parotid gland, and runs downwards and forwards in the neck to supply the platysma.

26. Accessory processes of parotid gland • Facial process — along parotid duct. It lies between zygomatic arch and the parotid duct • Pterygoid process — between mandibular ramus and medial pterygoid. • Glenoid process — between external acoustic meatus and temporomandibular joint • Poststyloid process

27. Blood Supply The parotid gland is supplied by the external carotid artery and its branches that arise within the gland. The veins drain into the external jugular vein and internal jugular vein.

28. Nerve Supply Parasympathetic nerves are secretomotor. They reach the gland through the auriculotemporal nerve. The preganglionic fibres begin in the inferior salivatory nucleus; pass through the glossopharyngeal nerve, its tympanic branch, the tympanic plexus and the lesser petrosal nerve; and relay in the otic ganglion . The postganglionic fibres pass through the auriculotemporal nerve and reach the gland.

29. Sympathetic nerves are derived from the plexus around the middle meningeal artery. These fibres start from lateral horn of T1 segment of spinal cord. These synapse in superior cervical ganglion. Postganglionic fibres travel along branches of external carotid, maxillary arteries and their branches . Sensory nerves to the gland come from the auriculotemporal nerve, but the parotid fascia is innervated by the sensory fibres of the great auricular nerve (C2, C3).

30. Lymphatic Drainage Lymph drains first to the parotid nodes and from there to the upper deep cervical nodes . Superficial nodes- lie underneath external parotid fascia 15-20 nodes embedded superficial to the facial nerve. Deep lobe may contain 1-2 nodes.

31. Parotid Duct/ Stenson’s Duct Parotid duct is thick-walled and is about 5 cm long. It emerges from the middle of the anterior border of the gland. It runs forwards and slightly downwards on the masseter.

32. RELATIONS Superiorly Accessory parotid gland The transverse facial vessels Upper buccal branch of the facial nerve Inferiorly The lower buccal branch of the facial nerve.

33. COURSE At the anterior border of the masseter, the parotid duct turns medially and pierces: a . The buccal pad of fat b . The buccopharyngeal fascia c . The buccinator ( obliquely) Because of the oblique course of the duct through the buccinator , inflation of the duct is prevented during blowing . The duct runs forwards for a short distance between the buccinator and the oral mucosa. Finally , the duct turns medially and opens into the vestibule of the mouth (gingivobuccal vestibule) opposite the crown of the upper second molar tooth

34. LANDMARKS OF FACIAL NERVE IN PAROTID SURGERY 1 . Conley’s Cartilaginous pointer - The nerve lies 1 cm deep and slightly anterior and inferior to the pointer. Cartilaginous pointer is a sharp triangular piece of cartilage of the pinna and “points” to the nerve. 2 . Tympanomastoid suture -Nerve lies 6–8 mm deep to this suture. 3 . Styloid process -The nerve crosses lateral to styloid process. 4 . Posterior belly of digastric - If posterior belly of digastric muscle is traced backwards along its upper border to its attachment to the digastric groove, nerve is found to lie between it and the styloid process.

35. SUBMANDIBULAR SALIVARY GLAND

36. INTRODUCTION This is a large salivary gland, situated in the anterior part of the digastric triangle. The gland is about the size of a walnut weighing about 15 to 20 g . It is roughly J-shaped, being indented by the posterior border of the mylohyoid which divides it into a larger part superficial to the muscle, and a small part lying deep to the muscle.

37. COVERINGS The gland is partially enclosed between two layers of deep cervical fascia. The superficial layer of fascia covers the inferior surface of the gland and is attached to the base of the mandible. The deep layer covers the medial surface of the gland and is superiorly to the mylohyoid line of the mandible

38. SUPERFICIAL PART This part of the gland fills the digastric triangle. It extends superiorly deep to the mandible up to the mylohyoid line. Inferiorly, It overlaps stylohyoid and the posterior belly of digastric. It has three surfaces: a. Inferior b. Lateral c. Medial

39. RELATIONS OF SUPERFICIAL PART The inferior surface is covered by : a. Skin b. Platysma c. Cervical branch of the facial nerve d. Deep fascia e. Facial vein f. Submandibular lymph nodes

40. The lateral surface is related to: a. The submandibular fossa on the mandible b. Insertion of the medial pterygoid c. The facial artery

41. The medial surface is related to: • Anterior part: Mylohyoid, submental branch of facial artery, mylohyoid nerve and vessels • Middle part: Hyoglossus , styloglossus , lingual artery, XII nerve • Posterior part: Stylohyoid, styloglossus , IX nerve

42. Deep Part This part is small in size. It lies deep to the mylohyoid, and superficial to the hyoglossus and the styloglossus . Posteriorly, it is continuous with the superficial part around the posterior border of the mylohyoid. Anteriorly, it extends up to the posterior end of the sublingual gland.

43. RELATIONS OF DEEP PART Present in between mylohyoid and hyoglossus . Laterally – Mylohyoid Medially – Hyoglossus Above – Lingual nerve with submandibular ganglion Below – Hypoglossal nerve

44. BLOOD SUPPLY AND LYMPHATIC DRAINAGE Arterial supply - Facial artery. The facial artery arises from the external carotid just above the tip of the greater cornua of the hyoid bone. The veins drain into the common facial or lingual vein. Lymph passes to submandibular lymph nodes

45. NERVE SUPPLY It is supplied by branches from the submandibular ganglion . These branches convey: 1 Secretomotor fibres 2 Sensory fibres from the lingual nerve 3 Vasomotor sympathetic fibres from the plexus on the facial artery

46. SUBMANDIBULAR DUCT/ WHARTON’S DUCT It is thin walled, and is about 5 cm long. It emerges at the anterior end of the deep part of the gland and runs upwards and forwards on the hyoglossus , between the lingual and hypoglossal nerves. At the anterior border of the hyoglossus , 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

47. SUBLINGUAL SALIVARY GLAND

48. INTRODUCTION This is smallest of the three salivary glands. It is almond shaped and weighs about 3 to 4 g. It lies above the mylohyoid, below the mucosa of the floor of the mouth, medial to the sublingual fossa of the mandible and lateral to the genioglossus.

49. RELATIONS Front– Meets opposite side gland Behind – Comes in contact with deeper part of submandibular gland Above – Mucous membrane of mouth Below – Mylohyoid muscle Lateral – Sublingual fossa Medial – Genioglossus muscles

50. DUCT, BLOOD AND NERVE SUPPLY About 15 ducts emerge from the gland. Most of them open directly into the floor of the mouth on the summit of the sublingual fold. A few of them join the submandibular duct. The gland receives its blood supply from the lingual and submental arteries. The nerve supply is similar to that of the submandibular gland . Lymphatic drainage- submental and submandibular lymph nodes.

51. ACCESSORY SALIVARY GLANDS Between 600 to 1000 in number, are small, isolated and numerous. Each gland has its own duct. Found to be anywhere in the mouth, especially concentrated in palate, floor of mouth and buccal areas.

52. MECHANISM OF SECRETION

53. AFFERENT STIMULATORY PATHWAYS 1) PSYCHIC STIMULI The thought and sight of food, and the sound and smells associated with cooking may be associated with increase in amount of salivation, while the thought of unrelished foods bring opposite effect. Psychosalivatory reflex- consequence of fear is the drying of mouth. 2) SMELL Several studies have established correlation between smell and salivation.

54. 3) TASTE Profuse salivation is stimulated by various taste stimuli of which most potent seems to be a mixture of acid and sugar, followed by acid, sweet and salt. 4) TACTILE STIMULATION Chewing and mastication are potent initiators of salivary production and excretion. Painful conditions such as aphthous ulcers, forceful tongue extraction or depression increase salivation. 5) INTERORGAN STIMULI Esophagosalivatory reflux results from irritation of distal esophagus . The stomach, liver, gall bladder and appendix may influence saliva production using the vagus nerve as a fferent pathway.

55. AFFERENT NEURAL PATHWAYS The pathways responsible forstimulatory sequence of salivation are located in 1 st , 5 th , 7 th and 9 th cranial nerves. These eventually connect through synaptic links with salivatory nuclei, responsible for salivation.

56. CENTRAL CONTROL OF SALIVATION The parasympathetic salivatory nuclei are located in pons and medulla. They are the superior and inferior salivatory nuclei. The former is responsible for stimulating submandibular and sublingual glands, and the later for stimulating the parotid. These nuclei are subject to influences from other parts of the brain.

57. EFFERENT PATHWAY Nerve stimulation is responsible in general terms for: ( a) secretory activity (b) the rate of blood flow and ( c) the contraction of myoepithelial cells . Parasympathetic pathway plays a major part in controlling secretory activity. When both sympathetic and parasympathetic pathways are used simultaneously, the effect on secretion appears to be synergistic . Changes in the composition of saliva may be influenced by the degree of activity of each of the two neural systems at any one time.

58. FORMATION OF SALIVA Saliva is the end product of a process of secretion in the acinus, which is then modified by the activity of the intercalated and striated ducts . The hydrostatic pressure in the capillaries surrounding the acini leads to the escape of water, ions, glucose, urea, amino acids and proteins of lower molecular weights into the interstices . The acinar epithelium is freely permeable to water and lipid- soluble substances, but less so to other products such as amino acids and glucose, which can gain entry only by active diffusion .

59. Stimulation of the secretomotor nerves causes the release of transmitter substances, namely, A cetylcholine for the parasympathetic fibres and N oradrenaline for the sympathetic. TRANSMITTERS

60. MECHANISM OF FORMATION OF SALIVA 1. Primary secretion of saliva. The acinar cells of salivary glands secrete the initial saliva into the salivary ducts. The initial saliva is isotonic, i.e. has the same Na+, Cl−, K+ and HCO − 3 concentrations as plasma. However , the initial saliva is soon modified by the salivary ducts.

61. 2. Modification of saliva The ductal cells that line the tubular portions of the salivary ducts change the composition of initial saliva by following processes: Reabsorption of Na+ and Cl− occurs in the ductal cells, therefore, the concentration of these ions is lower than their plasma concentration. Secretion of K+ and HCO3 − is caused by the ductal cells, therefore, the concentrations of these ions are higher than their plasma concentrations. Modified saliva becomes hypotonic in the ducts because the ducts are relatively impermeable to water.

62. EFFECTS OF FLOW RATE ON THE COMPOSITION OF SALIVA 1. At high flow rates , there is less time for reabsorption and secretion, and therefore the saliva is most like the initial secretion by the acinar cells. Thus, with the increase in flow rate the concentration of ions changes. 2. At low flow rates , there is more time for reabsorption and secretion, therefore, the modified saliva under resting conditions contains : Low concentration of Na+ (about 15–20 mEq /L) (Plasma-145 mEq /L) Low concentration of Cl− (15–20 mEq /L) (Plasma- 110 mEq /L) Low concentration of HCO3 − (10–15 mEq /L) (Plasma- 27 mEq /L)) High concentration of K+ (25–30 mEq /L ) (Plasma- 5 mEq /L)

63. PHASES OF SALIVARY SECRETION 1. Cephalic phase refers to the secretion of saliva before entering of food into the mouth. It is caused by a conditioned reflex initiated by the mere sight or smell of food. 2 . Buccal phase refers to the secretion of saliva caused by stimulation of buccal receptors by the presence of food in the mouth. It is an unconditioned reflex, partially regulated by the appetite area of the brain.

64. 3. Oesophageal phase occurs due to the stimulation of salivary glands to a slight degree by the food passing through oesophagus . 4 . Gastric phase refers to the secretion of saliva by the presence of food in the stomach. It specially occurs when irritant food is present in the stomach (e.g. increased salivation before vomiting). 5 . Intestinal phase refers to a salivary secretion caused by the presence of irritant food in the upper intestine.

65. FUNCTIONS OF SALIVA 1. PROTECTIVE FUNCTION Dilutes hot and irritant food substances Washes away food particles that remain in the oral cavity at the end of meal. Thus growth of microbes is prevented. Destroys harmful bacteria in the mouth by lysozymes, IgA and lactoferrin . Dilutes any HCl and bile which regurgitates into mouth.

66. 2. ROLE IN MASTICATION AND DEGLUTITION Lubricates the food, helps in bolus formation by acting as a glue. 3. DIGESTIVE FUNCTION Initial starch digestion starts by alpha amylase(ptyalin) present in saliva. Its role is limited by short duration of stay of food in mouth. When food is mixed with gastric juice, its acidity stops the action of salivary amylase.

67. 4. ROLE IN TASTE SENSATION Saliva acts as solvent for various foodstuffs. As taste is a chemical sense, the taste receptors respond only to the dissolved substances. 5. ROLE IN SPEECH Salivary mucus lubricates the oral mucosa and thus aids speech by facilitating movements of lips and tongue.

68. 6. ROLE IN TEMPERATURE REGULATION During state of dehydration, the salivary secretion is reduced which induces thirst. Panting mechanism:- in dogs, saliva is evaporated from the surface of tongue to cause evaporative heat loss.

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