Salivary glands role

seminar in periodontology about role of salivary glands and its secretion

1. Role of Salivary glands Prepared by: Ibrahim Muneim Hussein

2. Introduction The human salivary gland system can be divided into two distinct exocrine groups : The major salivary glands include the paired parotid, submandibular, and sublingual glands

3. minor salivary glands the mucosa of the upper aerodigestive tract is lined by hundreds of small, minor salivary glands 600-1,000 minor salivary glands line the oral cavity and oropharynx contributing a small portion of total salivary production

4. Parotid Gland   Anatomy The paired parotid glands are the largest of the major salivary glands and weigh, on average, 15–30 g. Located In the preauricular region and along the posterior surface of the mandible . . The parotid duct, also known as Stensen’s duct , secretes a serous saliva into the vestibule of the oral cavity. the anterior border of the gland, it travels parallel to the zygoma , approximately 1 cm below it, in an anterior direction across the masseter muscle. It then turns sharply to pierce the buccinators muscle and enters the oral cavity opposite the second upper molar tooth.

5. Submandibular Gland Anatomy The submandibular gland is the second largest major salivary gland and weighs 7–16 g The gland is located in the submandibular triangle, which has a superior boundary formed by the inferior edge of the mandible and inferior boundaries formed by the anterior and posterior bellies of the digastric muscle.

6. Wharton’s Duct The submandibular gland has both mucous and serous cells that empty into ductules, which in turn empty into the submandibular duct. The duct exits anteriorly from the sublingual aspect of the gland, coursing deep to the lingual nerve and medial to the sublingual gland. It eventually forms Wharton’s duct between the hyoglossus and mylohyoid muscles on the genioglossus muscle.

7. Sublingual Gland The smallest of the major salivary glands is the sublingual gland, weighing 2–4 g. Consisting mainly of mucous acinar cells, it lies as a flat structure in a submucosal plane within the anterior floor of the mouth,superior to the mylohyoid muscle and deep to the sublingual folds opposite the lingual frenulum . Several ducts of Rivinus from the superior portion of the sublingual gland either secrete directly into the floor of mouth, or empty into Bartholin’s duct that then continues into Wharton’s duct.

8. Minor Salivary Glands Unlike the major salivary glands, the minor salivary glands lack a branching network of draining ducts. Instead, each salivary unit has its own simple duct. The minor salivary glands are concentrated in the Buccal, Labial, Palatal, and Lingual regions. In addition, minor salivary glands may be found at the superior pole of the tonsils (Weber’s glands), the tonsillar pillars, the base of tongue (von Ebner’s gland) .

9. Minor Salivary Glands location

10. Physiology of Salivary Glands Saliva production, the main function of the salivary glands, is crucial in the processes of digestion, lubrication, and protection in the body. Saliva is actively produced in high volumes relative to the mass of the salivary glands, and it is almost completely controlled extrinsically by both the parasympathetic and sympathetic divisions of the autonomic nervous system . Saliva plays a crucial role in in the digestion of carbohydrates and fats through two main enzymes . Ptyalin α-amylase in saliva that cleaves the internal α-1,4-glycosidic bonds of starches to yield maltose, maltotriose, and α-limit dextrin. This enzyme functions at an optimal pH of 7, but rapidly denatures when exposed to a pH less than 4, such as when in contact with the acidic secretions of the stomach. Up to 75% of the carbohydrate content in a meal, however, is broken down by the enzyme within the stomach

11. The salivary glands of the tongue produce lingual lipase ,which functions to break down triglycerides. Unlike ptyalin, this enzyme is functional within the acidic stomach and proximal duodenum because it is optimally active at a low pH . Saliva also serves to dissolve and transport food particles away from taste buds to increase taste sensitivity . The mucus constituent of saliva facilitates the lubrication of food particles during the act of chewing, which serves to mix the food with saliva. Lubrication eases the processes of swallowing and of the bolus traveling down the esophagus. Salivary lubrication is also crucial for Speech . The antibacterial properties of saliva are due to its many protective organic constituents. The binding glycoprotein for immunoglobulin A (IgA), known as the secretory piece, forms a complex with IgA that is immunologically active against viruses and bacteria .

12. Function of Saliva At least 7 major functions of saliva have been identified Moistens oral mucosa. In fact, the mucin layer on the oral mucosa is thought to be the most important nonimmune defense mechanism in the oral cavity . Moistens dry food and cools hot food . Provides a medium for dissolved foods to stimulate the taste buds . Buffers oral cavity contents. Saliva has a high concentration of bicarbonate ions . Digestion . Alpha-amylase, contained in saliva, breaks 1-4 glycoside bonds, while lingual lipase helps break down fats. Controls bacterial flora of the oral cavity. Mineralization of new teeth and repair of precarious enamel lesions. Saliva is high in calcium and phosphate. Protects the teeth by forming a “Protective Pellicle”. This signifies a saliva protein coat on the teeth which contains antibacterial compounds. salivary flow rate play a more important role in oral hygiene than any of these factors

13. Xerostomia or dry mouth, due to lack of salivation, can lead to chronic buccal mucosal infections or dental caries . Comprised of both inorganic and organic compounds , saliva is distinguished by its high volume compared to salivary gland weight, high potassium concentration, and low osmolarity . The large relative volume of saliva production is due to its high secretion rate, which can go up to 1 ml per gram of salivary gland per minute . Saliva is mostly hypotonic to plasma, but its osmolarity increases with increasing rate of secretion, and at its highest rate saliva approaches isotonicity. The concentration of electrolytes in saliva also changes with varying secretion rates . Within the salivary gland, potassium (K+) concentration is always high while sodium (Na+) concentration is low compared to that found in plasma (noted that saliva is ALWAYS hypotonic to plasma) Effects of Aging Acinar cells do degenerate with age. However, total salivary flow rates have been found to be independent of age. Xerostomia, or the subjective complaint of dry mouth , must be distinguished from the objective finding of decreased salivary flow. Xerostomia in the elderly is generally either secondary to medications or to systemic disease . The Submandibular glands are more sensitive to metabolic and physiologic changes. Thus, it is salivary flow in the unstimulated state which is more greatly affected by such changes.

14. Other Systemic Conditions Sjogren's syndrome is a disorder of your immune system identified by its two most common symptoms — dry eyes and a dry mouth. The condition often accompanies other immune system disorders, such as rheumatoid arthritis and lupus. In Sjogren's syndrome, the mucous membranes and moisture-secreting glands of your eyes and mouth are usually affected first — resulting in decreased tears and saliva. Complications The most common complications of Sjogren's syndrome involve your eyes and mouth. Dental cavities. Because saliva helps protect the teeth from the bacteria that cause cavities, you're more prone to developing cavities if your mouth is dry. Yeast infections. People with Sjogren's syndrome are much more likely to develop oral thrush, a yeast infection in the mouth. Vision problems. Dry eyes can lead to light sensitivity, blurred vision and corneal damage.

15. Other Systemic Conditions Psychological stress conditions also induce significant changes in both salivary proteome and transcriptome. The increase of salivary amylase is a known proteomic indicator of psychological stress and sympathetic activation . A recent paper indicated that amylase specific salivary mRNA level also increases significantly after stress with some delay. Besides the above stress-markers, decrease of secretory IgA , and increase of immune-modulator defense protein salivary chaperone Hsp70 was also reported. Global profiling of genome, transcriptome and proteome present in saliva likely lead to the recognition of numerous other stress-markers and stress sensitivity markers in the next future

16. Other Systemic Conditions A number of other disorders exist, where salivary changes with significant diagnostic value were also characterized. In Cystic fibrosis the excretion of an unusual, less effective form of salivary epidermal growth factor (EGF ) was reported. There are also characteristic salivary changes in case of graft-versus-host disease including the elevated concentration of total protein, albumin, EGF, IgG, and a decreased amount of IgA and IgM in the saliva . In coeliac disease the elevated salivary level of IgA antigliadin antibodies (AGA) may be used for screening purposes with moderate sensitivity (60%) and high specificity (93%) . In case of peptic ulcers and chronic gastritis, Helicobacter pylori infection (a frequent cause) can be detected with 84% sensitivity and 82% specificity via detection of bacterial DNA in saliva . H. Pylori may also be detected with salivary antibodies against this bacterium (sensitivity 85%, specificity 55%) .

17. Virus Infections Saliva analysis is a good tool for detection of virus infections, based on identification of viral DNAs and RNAs, antibodies against viruses, and viral antigens . DNA and RNA analysis shows moderate to high sensitivity, however a progress related to the accuracy of such methods is very likely in the next future. Proteomic methods like detection of antibodies against viruses and detection of virus antigens are highly sensitive and specific methods available already today . Detection of salivary viral DNA is a possible diagnostic tool for screening with a moderate to high sensitivity in case of several viruses like cytomegalovirus (sensitivity 36% ), human herpes virus (HHV) type 6 (sensitivity 80% ), HHV type 7 (sensitivity 100%).

18. Dental Caries There are some more or less specific changes of salivary proteome, which may be used for recognizing caries-risk patients. These include decreased level of proline-rich proteins (PRP1 and PRP3), histatin 1 and statherin . Increased numbers of Streptococcus mutans and Lactobacilli in saliva were also associated with increased caries prevalence , and with the presence of root caries . Decreased complexity (fewer number of specii and phylotypes ) of the oral microbiota was also found to be a risk for early childhood caries . Although caries related microbiotal data were recognized mainly by analysis of tooth-surface biofilm (dental plaque) but the complex microbiota present in saliva likely reflect to this differences as well . Investigation of salivary microbiota with high capacity automatized nucleic acid extraction and analysis and also global genome, transcriptome and proteome profiling of saliva will likely lead to further new caries related predictive markers in the future

19. Periodontal Inflammation The presence of certain periodontopathogen bacterial species in saliva reflect their presence in dental plaque and periodontal pockets indicating that saliva may be a good tool to detect bacterial risk factors by salivary DNA analysis of oral microbiota . Such DNA-based methods open new perspectives in both the understanding and the diagnosis of periodontal disorders, since they allow the analysis of non cultivable (yet-to-be cultured) microorganisms as well . Besides genomic methods, proteomic analysis may also become important in the next future. It is known for example that the level of alpha-2-macroglobulin, alpha-1-antitripsin, elastase and also albumin in saliva may be good indicators of gingivitis and/or periodontitis. The level of salivary defense proteins like immunoglobulin, molecular chaperone Hsp70, cystatin S, salivary amylase, calprotectin, hystatins , lysozyme, lactoferrine , defensins , peroxidases, prolin -rich proteins and mucins may also have prognostic value related to the possible passing of gingivitis to periodontitis (where the latter is a more severe inflammation with irreversible destruction) . It is also likely that the global profiling of salivary genome, transcriptome and proteome will lead to recognition of further highly sensitive diagnostic markers of periodontal conditions.

20. Oral Candidiasis Saliva may also be used for detection of oral fungi . In case of oral candidiasis, salivary fungal counts may also reflect mucosal colonization . Alteration of salivary proteome related to proteins showing antifungal properties like immunoglobulin, calprotectine , histatin-5, mucins peroxidases, basic prolin -rich proteins, molecular chaperone Hsp70 etc. may also have important diagnostic/prognostic value especially in recurrent cases.

21. CONCLUSION Each of us may have inside our mouths a key to the pathological and disease biomarker library hidden inside our bodies. Saliva – the source of all this information – is the secretory product of glands located in or around the oral cavity. If we could read the stories of diagnostic information present within saliva, then the abundance of information waiting to be found could be comparable to a vast vault of information such as the internet. The relationship between salivation and behaviors within our daily lives is undeniable. Yet most people never appreciate the uniqueness of saliva. Efforts on the discovery of analytes in the saliva of normal and diseased subjects suggest an additional function of saliva, a local and systematic diagnostic tool. Analytes used for disease detection range from proteins, to antibodies, and nucleic acids that are of either human microorganism origins. Highly sensitive and high-throughput assays such as mass spectrometry, RT-PCR, microarray, and nano -scale sensors that can measure proteins and nucleic acids with a minimal amount of sample requirement in a short period of time allowed scientists to broaden the utility of saliva as a diagnostic tool.