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Saliva – composition and function

by Josephine Andrews
Published: Last Updated on 351 views

Saliva is secreted into the oral cavity by glands in the lining of the cheeks, palate, and throat. It lubricates bites of food so we can swallow them more easily. In addition, saliva contains digestive enzymes and is important for detecting taste. Read all about saliva!

What is saliva?

Saliva is the odorless and tasteless secretion of the salivary glands in the oral cavity. It is mainly formed by three large glands: the bilateral parotid gland (parotid gland), the submandibular salivary gland (submandibular gland), which is also bilateral, and the sublingual salivary gland (sublingual gland).

There are also numerous small salivary glands in the mucous membranes of the cheeks, palate and throat and in the base of the tongue.

saliva composition

The body produces around 0.5 to 1.5 liters of saliva per day. Composition of the secretion depends on the producing gland:

  • The parotid gland produces “diluting saliva,” a thin, low-protein secretion that makes up about a quarter of the total amount of saliva.
  • The submandibular salivary gland forms a clear, protein-containing and slightly stringy “gliding saliva” that accounts for about two-thirds of the daily amount of saliva produced.
  • The sublingual salivary gland supplies a protein-rich, stringy “gliding saliva”.

A liter of saliva contains a total of around 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).

Ammonia, uric acid and urea , some folic acid and vitamin C are also found in the saliva . Electrolytes like sodium and potassium are also included.

Digestive enzymes are also found in saliva. The most important representative is alpha-amylase (ptyalin), which can break down carbohydrates (starch). It is produced and secreted almost exclusively by the parotid gland – in an amount that would be sufficient to digest all of the starch ingested. However, there is not enough time for this because the bites of food are swallowed relatively quickly (along with the enzyme). In the stomach , salivary amylase is inactivated by acidic gastric juice. The amylase from the pancreas then has to take care of the further carbohydrate splitting in the small intestine .

Another enzyme found in saliva is lipase , which breaks down fat and is secreted by the lingual glands. This enzyme is of particular importance for infants, specifically for digesting 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). Smell and taste stimuli (such as a good smell of roast meat or lemon ), feelings of hunger and psychogenic factors also trigger salivation.

When we sleep or are dehydrated, little saliva is secreted.

What is the function of saliva?

Saliva has several jobs:

  • It is a solvent for nutrients that can only be recognized by the taste receptors in the tongue when dissolved.
  • Mucins, the “lubricants” of the oral cavity, make it easier to chew and swallow solid food components. In addition, the mucous film they form on the oral cavity wall protects the underlying cell layer (epithelium) from injury and drying out.
  • It contains digestive enzymes such as fat-splitting lipase and carbohydrate-splitting ⍺-amylase.
  • Other enzymes included are lysozyme and peroxidase. Lysozyme can break down bacterial wall components ; Peroxidase has non-specific antibacterial and antiviral properties.
  • Immunoglobulin A (IgA) is also found in the saliva : This type of antibody can fight off pathogens.
  • Saliva moistens the oral cavity, which is important for clear pronunciation.
  • He keeps the mouth clean by constantly rinsing the oral cavity and teeth .

What problems related to saliva can occur?

Acute parotid gland inflammation ( parotitis ) is caused by viruses or bacteria. The mumps virus is a common reason for painfully swollen parotid glands. However, parotitis can always recur, i.e. it can occur chronically and recurrently. The reason for this has not yet been finally clarified.

A tumor can develop in the area of ​​the salivary glands. Such a salivary gland tumor can be benign or malignant (cancerous).

If the composition of the saliva changes as a result of an illness or medication, a salivary stone can form – a hard calculus made up of components of the gland secretion. Salivary stones can block the duct of a salivary gland, causing the gland to swell.

Salivary cysts can be congenital enlargement of the glands or can result from salivary blockage due to a stone.

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