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