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Functional Anatomy of Oral Cavity
This Sqadia video demonstrates about Salivary Secretion. Saliva is secreted in oral cavity. Oral cavity is otherwise known as buccal cavity or mouth. The oral cavity includes the lips, gingivae, retromolar trigone, teeth, hard palate, cheek mucosa, mobile tongue, and floor of the mouth. Two major functions performed by mouth are ‘Mechanical Digestion’ and ‘Mixing Food with Saliva’. The rate of saliva secretion varies from 0.1 – 4ml/min depending on the degree of stimulation. The function of saliva are reflected by its constituents. Mucins serve to lubricate the food, making it easier to swallow. Saliva dissolves compounds in food. Saliva also contains alpha-amylase, which starts the digestion of starches in the mouth, while immunoglobulin A and lysozyme are part of the immune defense system.
In humans, the saliva is secreted by three pairs of major salivary glands and some minor salivary glands. Major glands are:
- 1. Parotid glands
- 2. Submaxillary or submandibular glands
- 3. Sublingual glands.
Parotid glands are the largest of all salivary glands but secretes 25% of total saliva. These glands are situated at the side of the face just below and in front of the ear. Submaxillary Glands is the intermediate gland in size and secretes 60% of total saliva. These glands are located in submaxillary triangle, medial to mandible. Sublingual Glands are the smallest salivary glands and secretes 25% of total saliva. These are situated in the mucosa at the floor of the mouth. Minor glands lie just under mucosa. These are distributed over lips, cheeks, palate, floor of mouth & retro-molar area. Minor glands include Glands of Von Ebner, also known as serous fluid producing glands. These are located on posterior aspect of tongue. The ducts of the salivary glands allow the passage of salivary juice from the glands to the oral cavity. Salivary glands contain tube like structure for conveying secretion called duct. The ducts of the salivary glands allow the passage of salivary juice from the glands to the oral cavity. The ducts of salivary glands are Stenson Duct, Wharton Duct, and Duct of Rivinus. A number of diseases can affect salivary glands, such as Xerostomia, Sialolithiasis, Sjogren’s Syndrom, Salivary Fistula, and Mumps Virus.
Composition and Functions of Saliva
Major components of saliva are mucus, amylase, lingual lipase, electrolyte solutions, proteins and enzymes. Daily secretion of saliva ranges from 800-1500ml and pH ranges between 6 and 7. Saliva is a very essential digestive juice. It has many functions.
Formation of Saliva
Salivary glands consist of clustered secreting acini end pieces attached to freely branching ductal system. Three types of ducts are present in the branched ductal system of all salivary glands: Intercalated ducts, Striated ducts, and Excretory ducts. Intercalated ducts contain low cuboidal epithelium and a narrow lumen. Striated ducts contain more columnar cells. Excretory ducts have cuboidal epithelium with stratified squamous epithelium lining the terminus. Saliva is formed in 2 steps: 1. Initial Saliva Production by Acinus, 2. Modification of Initial Saliva in Ducts. Primary Secretion Contains ptyalin, mucus and ions. It is similar to plasma in concentration of ions. In ductal Reconditioning, absorption of Na+ and Cl- takes place, and, K+ and HCO3- are secreted.
Regulation of Saliva
Salivary secretion is regulated only by nervous mechanism. Control of salivary secretion is neural only. Autonomic nervous system is involved in the regulation of salivary secretion. Salivary glands are supplied by both parasympathetic and sympathetic divisions of autonomic nervous system. Parasympathetic regulation produces a large volume of watery saliva rich in enzymes. It is because the parasympathetic fibers activate the acinar cells and dilate the blood vessels of salivary glands. Sympathetic regulation produces a large volume of watery saliva rich in enzymes. It is because, these fibers activate the acinar cells and cause vasoconstriction.