There are several salivary glands in the mouth, the most important of which are the parotid gland and the submandibular gland in addition to the sublingual gland. In addition to these three types of glands, there are several other small salivary glands which also specialize in secreting saliva in the mouth but to a lesser extent than the three salivary glands that are mentioned above.
The parotid gland and the submandibular glands are situated outside the oral cavity. They secrete saliva which reaches the oral cavity through canals that connect the glands with the openning of the mouth.
The parotid gland is situated below the skin in front and below the ear in the temporal region of the head. The submandibular gland is situated below the floor of the mouth. The sublingual salivary gland is situated in the floor of the mouth in front of the submandibular gland.
The salivary glands usually secrete saliva into the oral cavity in response to stimulation of the nerves in the salivary glands by the parasympathetic division of the autonomic nervous system. The parasympathetic stimulation leads to increased secretion of saliva from these glands.
The sympathetic division of the autonomic nervous system has the opposite effect. It reduces the amount of secretion of saliva from the various salivary glands. Stressful situations can lead to dry mouth due to the effect of sympathetic nerves on the salivary glands.
Anticholinergic drugs such as those used to treat certain medical conditions such as heart problems can lead to dryness of the mouth due to the suppression effect on the parasympathetic nervous system.
The saliva which is the secretory product of the salivary glands has several functions. One of them is protective as well as digestive function. The salivary glands under normal conditions secrete daily more than a liter of saliva to the mouth. Its function is related to metabolism as well as non metabolic function.
The salivary secretion in the mouth helps to moisten the mucosa of the mouth. In addition it functions by moistening the food in the mouth. Thus preparing it for swallowing. The salivary secretion is basic containing high concentration of bicarbonate ions.
Thus one of the functions of saliva is to control the pH of food in the mouth that is ingested into the stomach. The saliva also contains enzymes that help in digesting carbohydrates. This enzyme is called amylase. It functions by breaking 1-4 glycosidic bonds in carbohydrates.
This action of digesting carbohydrates supplementary to the major digesting function of carbohydrates which takes place in the small intestine through the action of the amylase enzyme that is secreted by the exocrine pancreas to the duodenum.
The saliva also contains enzymes that can degrade and neutralize bacteria in the mouth. This enzyme is called lysozyme. Saliva also washes harmful bacteria is then swallowed into the offensive acidic environment of the stomach that can kill the bacteria.
The saliva also contains high concentration of the ions calcium and phosphate. Thus helping in the mineralization process of teeth. Saliva also contains potassium ions with a concentration that is much higher than that in the blood. In addition, it contains little sodium ions as well and some other ions such as chloride and thiocyanate and phosphorus.
Disorders of the salivary glands include the presence of stones in the glands. It occurs most often in the submandibular gland possibly due to its thicker than usual salivary secretion. Obstruction of the salivary gland can cause an inflammatory process.
Another disorder that can affect the salivary glands as well as tear glands is called sjoegren syndrome. This is an autoimmune disorder in which secretions by the salivary gland as well as from the tear glands is stopped. Thus contributing to dry eyes and dry mouth.
Patients that have sjoegren syndrome often have also associated with it other autoimmune disorders notably rheumatoid arthritis. Mumps is another viral infection that can affect the parotid glands. It is characterized by swelling of the gland in addition to throat pain.