What are salivary glands?
The salivary glands are made up of 3 pairs of major glands – the parotid, submandibular and sublingual glands – and numerous (up to 1000) minor salivary glands located in the oral cavity and pharynx.
The parotid gland is the largest of the salivary glands, located between the ascending ramus of the mandible and the mastoid process. The parotids produce mainly serous saliva. The parotid duct passes forwards from the gland across the masseter muscle and opens into the mouth via a small papilla on the buccal membrane opposite the second upper molar tooth. The facial nerve passes through the gland and divides into five main branches as it passes forwards.
The submandibular glands lie beneath and in front of the angle of the jaw. The submandibular duct opens into the floor of the mouth with its orifice just lateral to the frenulum of the tongue. A mixture of serous and mucinous saliva is produced from these glands.
The sublingual gland is the smallest of the major salivary glands and lies just deep to the floor of the mouth mucosa between the mandible and genioglossus muscle. Unlike the parotid and submandibular glands, the sublingual gland has no true fascial capsule, nor does it have a single dominant duct. Instead, there are several small ducts that produce mainly mucinous saliva from the gland into the floor of the mouth.
What is the purpose of saliva?
Saliva has several important functions, including lubricating and binding food, facilitating swallowing, keeping the mouth moist which aids speech, acting as a solvent for molecules in food which facilitate taste, and maintaining oral hygiene (helps to wash away bacteria around teeth, contains immunoglobins such as IgA and also enzymes which break down starch). It is estimated that humans produce over half a litre of saliva each day.
When do they cause problems?
Infection
Acute parotitis is usually a viral infection (e.g. mumps). In children, parotitis may be recurrent. Acute infection of any of the salivary glands may be retrograde from infection in the mouth, or following extensive dental treatment. Tumours of the salivary glands may present as an acute infective episode. Acute inflammatory obstruction of the sublingual gland may cause a mucocoele or ranula that presents as an acute swelling of the floor of the mouth, under the tongue.
Stones
These occur more commonly in the submandibular gland than the other salivary glands. The onset is usually an acute swelling of the gland associated with eating, followed by recurrent bouts of swelling at mealtimes. First line investigations include plain x-ray (most calculi are radio-opaque) and ultrasound scanning. Sialography is occasionally performed, where the ducts of the parotid or submandibular salivary glands may be cannulated and contrast injected.
Tumours
80% occur in the parotid gland, of which 80% are benign, and of these, 80% are pleomorphic adenomas. There is a small risk of malignant transformation in pleomorphic adenomas (over 10 yrs = 6%; over 15 yrs = 10%; over 20 yrs = 15%). Malignant signs include pain, rapid growth, facial nerve paralysis, fixation, ulceration and nodal metastasis.
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