What is saliva?
Saliva is the odorless and tasteless secretion of the salivary glands in the oral cavity. It is mainly produced by three large glands: the bilateral parotid gland (parotid gland), the submandibular gland (submandibular gland) and the sublingual gland (sublingual gland).
In addition, there are numerous small salivary glands in the buccal, palatal and pharyngeal mucosa and in the base of the tongue.
Saliva composition
The body produces about 0.5 to 1.5 liters of saliva per day. Composition of the secretion depends on the producing gland:
- The parotid gland produces “dilution saliva,” a thin, low-protein secretion that makes up about a quarter of the total saliva.
- The mandibular salivary gland produces a clear, protein-rich and weakly filamentous “lubricating saliva” that accounts for about two-thirds of the amount of saliva produced daily.
One liter of saliva contains a total of about 1.4 to 1.6 grams of protein as mucus (mucin) in the form of mucoproteins (proteins with a carbohydrate content). Mucins form the mucus film on the wall of the oral cavity (as well as the esophagus, stomach and intestines).
Also found in saliva are ammonia, uric acid and urea, some folic acid and vitamin C. Electrolytes such as sodium and potassium are also present.
Another enzyme in saliva is lipase, which splits fat and is secreted by the lingual glands. This enzyme is of particular importance for infants, specifically for the digestion of the fat contained in breast milk. This milk fat covers a large part of the energy needs of babies.
Secretion of saliva
The secretion of saliva is reflexively triggered by chemical irritation of the oral mucosa (contact with food) and by mechanical stimuli (chewing). Olfactory and gustatory stimuli (such as a good roasting smell or lemon), hunger pangs, and psychogenic factors also trigger salivary flow.
When we are asleep or dehydrated, little saliva is secreted.
What is the function of saliva?
Saliva has several functions:
- It is a solvent for food substances, which can only be recognized in dissolved form by the taste receptors in the tongue.
- It contains digestive enzymes such as the fat-splitting lipase and the carbohydrate-splitting ⍺-amylase.
- Other enzymes contained are lysozyme and peroxidase. Lysozyme can cleave wall components of bacteria; peroxidase has non-specific antibacterial and antiviral properties.
- Saliva also contains immunoglobulin A (IgA): this type of antibody can ward off pathogens.
- Saliva moistens the oral cavity, which is important for clear pronunciation.
- It keeps the mouth clean by continuously rinsing the oral cavity and the teeth.
What saliva-related problems can occur?
Acute parotitis is caused by viruses or bacteria. For example, the mumps virus is a common cause of painfully swollen parotid glands. However, parotitis can also recur again and again, i.e. it can be chronic recurrent. In this case, the cause has not yet been conclusively clarified.
If the composition of saliva changes, for example as a result of illness or medication, a salivary stone can form – a hard concretion made up of components of the gland secretion. Salivary stones can block the excretory duct of a salivary gland, causing the gland to swell.
Salivary cysts may be congenital gland enlargements or may result from the accumulation of saliva due to a stone.
