Functions of Saliva

• Saliva is a secretion of salivary glands.
• Contains maximum water content (99.5%) and 0.5% solids.
• Includes solid content like organic, inorganic and gases also.
• Various important functions which leads to many inconveniences if absent.

A) Swallowing of food

• Moistening of food occurs when food is taken from mouth.
• Dissolving of food also assisted by saliva.
• Besides above function chewing is also facilitated.
• Food moistened and masticated is thus moved by tongue.
• Converts food to bolus by rolling.
• Swallowing is facilitated by mucin present in saliva which acts as lubricants.

B) Appreciation of taste

• Solvent action of saliva helps to identify taste sensation.
• Taste is a chemical sensation.
• Chemicals in solid food get dissolved in saliva which stimulates the taste buds.
• Thus, taste is recognized by the stimulated taste bud.

C) Digestive function

• Three vital digestive enzymes are contained by saliva.
• Salivary amylase, maltase and lingual lipase are the major enzymes.

Salivary amylase

• Is a carbohydrate-digesting enzyme also called amylolytic enzyme.
• Function more in boiled starch or cooked form.
• Starch converts to dextrin and maltose.
• In mouth, digestion of starch initiates but for short time.
• Major digestion takes place in stomach as stomach hold food longer than mouth.
• Optimum pH of 6 activates salivary amylase.
• But, this enzyme cannot act on cellulose.

Maltase

• Only traces of maltase are present in human saliva.
• Maltose is acted upon and is converted to glucose.

Lingual lipase

• Enzyme that digests lipid also called lipid digesting (lipolytic) enzyme.
• Serous glands secrete this enzyme.
• Located on the posterior aspect of tongue.
• Pre-emulsified fats i.e., milk fats generally digested by this enzyme.
• Triglycerides are acted upon to convert to fatty acids and diacylglycerol.

D) Protective and cleansing functions

• Rinses mouth and teeth constantly as it is secreted constantly.
• Food debris is kept away.
• Epithelial and foreign particles are shedded.
• Thus, bacterial growth is kept away as these things can act as a culture media.
• An enzyme is present in saliva called lysozyme.
• This enzyme kills bacteria like Staphylococcus, Streptococcus and Brucella.
• Antimicrobial property is present in saliva content i.e., proline-rich proteins.
• These proteins neutralize toxic substances like tannins.
• Tannins are substances found in fruits and many other food substances.
• Antimicrobial property is also shown by lactoferrin content.
• Enamel formation is stimulated by lactoferrin and proline-rich proteins.
• Thus, teeth remains protected.
• Antibacterial and antiviral property also found as saliva contains IgA.
• Mucus membrane of mouth remains protected by mucin content of the saliva.

Image source: researchgate

E) Role in speech

• Moistens and lubricates soft parts of the mouth, lips.
• Thus, this function of saliva helps in speech.
• Dry mouth does not allow proper articulation and pronunciation.

F) Excretory function

• Organic as well as inorganic substances are excreted in saliva.
• Substances like mercury, lead, thiocyanate, potassium iodide.
• Some viruses are excreted such as those causing rabies and mumps.
• Saliva also secretes those substances that it does not secrete in normal conditions.
• Only in pathological conditions they are secreted.
• Glucose is secreted in diabetes mellitus condition.
• Not only that some saliva constituents are excreted in large quantities.
• Excess urea is excreted in nephritis from saliva.
• Likewise in hyperparathyroidism, excess calcium is excreted.

G) Body temperature regulation

• Dripping of saliva occurs excessively in some animals like dogs and cattles.
• This happens during panting that help them to loss heat.
• Thus, temperature of body is regulated.
• However, sweat glands help in maintaining body temperature in humans.
• There is no role of saliva in this case.

H) Regulation of water balances

• Salivary secretions decrease when the content of body water decreases.
• Thirst is thus induced as dryness of the mouth results.
• Water after taken quenches the thirst.
• This maintains the water level which gets stored again.

  Image source: biologydictionary

References: 

i) https://www.lion.co.jp/en/oral/role/03.htm#:~:text=When%20we%20chew%20thoroughly%2C%20the,prevention%20of%20caries%20and%20gingivitis.

ii) https://pubs.rsc.org/en/content/chapterhtml/2022/bk9781788017152-00001?isbn=978-1-78801-715-2&sercode=bk

iii) https://www.sciencedirect.com/science/article/abs/pii/S2468519420301026

Functions of Saliva