The Mouth or Oral Cavity

is the common entrance to the digestive and respiratory tracts. It serves as the site of entry for foodstuffs into the body, for the initial processing or mastication of those foodstuffs and also, as a site for articulation in speech and as an alternate airway.

Anatomically, the mouth is delimited anteriorly by the lips and posteriorly by the anterior tonsillar pillars. The roof of the mouth is formed by the hard and soft palates. The floor of the mouth by the tongue, a muscular structure that contains the organs of taste found in the taste buds and the mucosa, overlying the sublingual and submandibular salivary glands. The walls are lined by the buccal mucosa.

ORAL PHYSIOLOGY The mouth, one of the main openings of the body, is the unique organ for ingestion of food and water (including secretion of saliva, mastication and swallowing), taste and communication, and also has several other functions listed below: 1. Ingestion of the food and water 2. Secretion of saliva 3. Digestion 4. Mastication (chewing) 5. Swallowing 6. Taste 7. Communication and Speech 8. Body defense 9. Breathing 10. Thirst 11. Absorption 12. Excretion 13. Judging the temperature and texture of foods.

I. INGESTION OF THE FOOD AND WATER The mouth is the unique organ for eating and drinking which are essential and indispensable for the life. If one cannot eat and drink as it happens during coma he will die in a short time especially because of dehydration unless he is fed intravenously.

II. SECRETION OF THE SALIVA A. Salivary Glands The saliva is the secretion a group of glands placed in the tissues forming the mouth called salivary glands. 1. Parotid gland: The parotid gland is the largest salivary gland and is found wrapped around the mandibular ramus. The secretion produced is mainly serous in nature and enters the oral cavity via Stensen's duct.

2. Submandibular glands: The submandibular glands are a pair of glands located beneath the lower jaws, superior to the digastric muscles. The secretion produced is a mixture of both serous fluid and mucus, and enters the oral cavity via Wharton's ducts. Approximately 70% of saliva in the oral cavity is produced by the submandibular glands, even though they are much smaller than the parotid glands.

3. Sublingual glands: The sublingual glands are a pair of glands located beneath the tongue, anterior to the submandibular glands. The secretion produced is mainly mucus in nature. Approximately 5% of saliva entering the oral cavity comes from these glands.

4. Minor salivary glands: There are over 600 minor salivary glands located throughout the oral cavity within the submucosa of the oral mucosa. Their secretion is mainly mucous in nature and has many functions such as coating the oral cavity with saliva. Problems with dentures are usually associated with minor salivary glands.

Functions of the Saliva: It adjusts the heat of the cold and hot foods to the body temperature. 1. Digestion: It starts carbohydrate digestion through the enzyme ptyalin (alpha-amylase) and breaks cooked starch into disaccharides. 2. Swallowing: a. It wets the dry foods in order to ease swallowing. b. Lubrication and binding: The mucus in saliva binds masticated food pieces together to form a slippery bolus that slides easily through the esophagus. 3. Protection of the mucosa: Mucus coats the oral cavity and esophagus so that the food never directly touches and damages the epithelium.

4. Oral hygiene: a. Mechanical cleaning: i. The saliva itself washes away pathogenic bacteria, the remnants of food that provide metabolic support to the bacteria, and dead epithelial cells. (In infectious diseases with high fever, the saliva secretion decreases. In turn, the surface of the tongue is covered with pus composed of dead epithelial cells, bacteria and leucocytes which prevents the sensation of taste and causes an unpleasant taste whatever the person eats.) ii. The washing away of the food remnants is also important since floral bacteria in the mouth cause acid production by fermentation of carbonhydrates that leads dental cares.

b. Saliva contains several factors that destroy bacteria: i.Thiocyanate ions which become bactericidal after entering the bacteria. ii.Several proteolytic enzymes -most important, lysozyme- that attack the bacteria, aid the thiocyanate ions in entering the bacteria and digest food particles, thus helping further to remove the bacterial metabolic support. iii.Antibodies (secretory IgA) that can destroy oral bacteria including some that cause dental caries. (In the absence of salivation, oral tissues often become ulcerated and otherwise infected, and caries of the teeth can become rampant.) 5. Taste: It solubilizes the dry foods so that they can stimulate the taste buds.

6. Speech: It wets the oral mucosa so that the person can speak easily (for this reason, during a long speech the speaker needs to drink some water several times). 7. Thirst: Dryness of the oral mucosa initiates thirst reflex which stimulates the thirst center in hypothalamus. Thus the person needs and drinks water. If a person loss excess water because of sweating, diarrhea, poliuri or hemorrhage, the saliva secretion decreases and the oral mucosa becomes dry that leads thirst. 8. Excretion: Hg, Kl, Pb, urea and some viruses such as rabies and mumps virus excreted in the saliva.

 The average daily the avarage volume of saliva production is ml  This represents about 1/5 of the total plasma volume  This fluid is not lost as most of it is swallowed and reabsorbed by the gut.  In a healthy mouth, the mean volume of saliva ranges from approximately 1.07 mL /minbefore swallowing to approximately 0.77 mL/min after swallowing.

 Salivary flow varies in the stimulated (eg, chewing) and unstimulated state. Stimulated flow contributes up to 90% of average daily saliva production, at a rate of between 0.2 and 7 mL/min, while normal flow in the unstimulated state is > 0.1 mL/min  The greatest volume of saliva is produced before, during and after meals, reaching its maximum peak at around 12.a.m. and falls considerably at night, while sleeping.  Several physiological and pathological conditions can modify saliva production quantitatively, e.g. smell and taste stimulation, chewing, psychological and hormonal status, drugs, age, hereditary, oral hygiene and physical exercise.

 All the salivary fluid is produced from the local vascular bed in the acinar region, and is transported through the duct system,  The excess sodium and chloride are reabsorbed and some additional proteins are secreted, and then empties into the oral cavity.  A sodium gradient that is actively generated within the secretary end piece causes fluid to flow into the lumen through the tight junctions between the acinar cells

THE SECRETORY UNIT The basic building block of all salivary glands ACINI - water and ions derived from plasma Saliva formed in acini flows down DUCTS to empty into the oral cavity.

TWO STAGE HYPOTHESIS OF SALIVA FORMATION Water & electrolytes Isotonic primary saliva Most proteins Some proteins electrolytes Na + Cl - resorbed K + secreted Hypotonic final saliva into mouth