The salivary glands are exocrine glands that are positioned in and around the oral cavity and secrete their salivary contents into the mouth to help keep the oral mucosa protected and lubricated as well as to help in the initial stages of digestion during mastication of food so that a food bolus is created and ready to be swallowed for further processing. They are divided into the major and minor salivary glands and the difference between them is that firstly the major ones are much larger in size and are a collection of exocrine tissue that secretes as a whole into a salivary duct rather than acting individually and therefore end up producing a much larger amount of saliva per day than the minor ducts. The main role of the minor glands is to lubricate the oral cavity, while digestive and protective saliva is produced by the major glands.
Saliva is a seromucinous liquid that has several major functions within the oral cavity which include lubrication, digestion, antimicrobial action, buffering, hormone regulation and taste sensation. It contains 99.5% water and the rest is electrolytes, mucus, glycoproteins, enzymes and antibacterial compounds. There are two major types of saliva that are secreted from the salivary glands and they are serous and mucinous. The submandibular gland is the only mixed salivary gland that secretes both types in a 3:2 ratio of serous to mucous respectively. The parotid gland is the only gland that secretes purely serous saliva, while the sublingual gland and minor salivary glands secrete purely mucinous saliva. The total daily output of saliva in an adult is between one and one and a half liters of saliva.
The Major Glands
The parotid gland is the largest of the major salivary glands and it sits bilaterally in between the ramus of the mandible and the sternocleidomastoid muscle. It produces between twenty five and thirty percent of the total daily salivary output which is released through Stensen’s duct whose orifice can be seen on the buccal wall at the level of the maxillary second molar. The submandibular gland is the second largest of the major salivary glands and like all three of them it is a paired gland. It produces by far the largest amount of saliva of all and account for seventy percent of the total daily output. Wharton’s duct opens at the sublingual papilla under the tongue. Lastly, the sublingual gland is the smallest of the major salivary glands and is unique in the fact that it has several ductal openings that run along the sublingual folds. It also secretes the smallest portion of saliva per day out of the major glands at just five percent.
The Minor Glands
The minor salivary glands account for approximately one percent or less of the total daily salivary output. They can be found in patches around the oral cavity such as the bucca, the labia, the lingual mucosa, the soft palate, the lateral parts of the hard palate, the floor of the mouth and between the muscle fibers of the tongue. They amount to approximately one thousand individual glands in total.
Salivary gland cysts can develop due to injuries, tumours, infections or salivary stones that can block the flow of saliva. Since it cannot escape into the ducts it remains within the tissues which start to swell as the saliva builds up. It is usually painless but can cause problems when eating or speaking. Removal of the underlying cause will correct the problem and recurrence is uncommon.