Saliva - 1

Saliva is a colourless, slimy, fluid secreted into the mouth from salivary glands. Normally it is secreted continuously for 24 hours, 7 days. Unknowingly, we are swallowing it with food/drinks or alone to wet the throat. It amounts to about 700–1,000 ml per day. Even though saliva is secreted round the clock (like tears), it is not felt unless otherwise it is secreted in excess or less in quantity or quality.

Everyone swallows saliva regularly (unknowingly). But one might feel bad when it is secreted more or when it is tough and stringy in early morning (due to drying of mucous saliva).We can realise the secretion of saliva when we are still or sleepy. Drooling saliva may be indicative of stunning (after a magical performance, good food, etc.) or feeling drowsy. Even though saliva can smell bad after drying (due to bacteria and cells), its functions are really useful to the body. Knowing all its worthy functions and essential need, people might resist rewarding (spitting) it to others after watching a bad performance or to shame someone.

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Also some find it an unwanted, nasty fluid and constantly keep spitting it out. Some others may develop the habit of spitting saliva with betel nut chewing or tobacco chewing or to clear the throat. Spitting not only makes the environment horrible, it also makes body fluids go waste.

Composition of saliva - Saliva is mainly composed of water (90-98 per cent), mucous, electrolytes (sodium, potassium, chlorides, bicarbonates, magnesium, phosphates, calcium, etc), enzymes, cells, bacteria, etc., constitute the rest. PH of saliva seems to be mostly neutral or slightly alkaline (6.4).

Functions of saliva – Saliva has innumerous functions. Saliva works as

• Moisturiser – saliva keeps the mucous membrane of cheek, lips, tongue and throat moist and slippery to gulp food easily.

• Solvent and taste promoter – Saliva dissolves the food substances placed in the mouth to promote and identify the taste (taste buds cannot identify the taste of dry substances)

• Cleansing agent – it wipes and cleans cheek, teeth, gums, lips and throat with the help of tongue, to maintain cleanliness and odour-free mouth.

• Anti-bacterial – Saliva can resist bacteria. Enzymes in the saliva work for it.

• Wound healer – Wound seems to heal fast with saliva (unless it is more acidic)

• Pain-killer – Saliva can soothe pain too.

• Thirst enhancer – (drying) Saliva also remains as an indicator for the brain to call for water needed for the body (since low volume of water in the body causes less volume of saliva)

• Digestive agent – generally digestive function starts in the mouth itself – grinding, dissolving, making food into bolus, etc., are all part of the digestive functions. Saliva is the first digestive juice of digestive tract. It breaks down the food substances for easy digestion.

• Excretory functions – Saliva has excretory functions too. Salivary duct adjusts the composition of saliva according to the need of the body and also expels the unwanted or overloaded electrolytes or chemicals or bacteria (in rabies, chicken pox, etc., saliva can be infectious).

• Protective functions – Spreading as a layer all over the mucous membrane of mouth acts as protective coat against abrasions or entry of infection.

• Spit – It helps in spitting out the unwanted food or foreign substances (stones in foods, insects, etc.) which have entered into the mouth unknowingly.

• Neutraliser – Saliva having PH around 6.4 (slightly alkaline) with increased secretion can help in controlling heartburn/oesophagitis/acidity of stomach (natural care against these conditions).

• Finally, without saliva, no one can speak fluently.

Variation of saliva secretions – saliva secretions may vary depending upon various factors and substances being taken in. Generally, males have more secretion than females.

Factors which promote more secretion

• Age - saliva secretions will be more in childhood

• Chewing / mastication / speaking can increase it

• Sour things / tasty food substances

• Meal time

• Sight or thought of good food

• Pregnancy

• Sialorrhoea (increased secretion of saliva in disease conditions like rabies, polio, tumours of face, Parkinsonism, schizophrenia, stammering, paralysis, etc.)

• Chewing bubble gum / betel nut leaves/ tobacco / mint, etc.

Factors which lessen saliva secretions are:

• Age – elderly people will have less secretions (and taste too)

• Sleep – naturally reduces it as there is no requirement (other than as moisturiser)
  Dirty plates / circumstances / environment (nasty smelly area) can inhibit it.

• Dehydration of the body or low intake of water

• Depression / anxiety / stress / tension / fear

• Vigorous exercises

• Drugs and treatment can cause mouth dryness (for example – antibiotics, chloroform, radiation therapy, chemotherapy, etc.)

Salivary glands – The salivary glands are 3 pairs in number namely:

• Parotid glands – which constitute 25-30 per cent of total volume of saliva

• Sub-mandibular glands – which constitute 70-75 per cent of the total volume of saliva

• Sub-lingual glands – which constitute 5-10 per cent of the total volume of saliva

Parotid glands – are situated just behind the jaw and just below the ears on each side (back of cheek). It is the largest gland among the salivary glands. They secrete mainly watery saliva (i.e., of serous type).

Sub-mandibular glands – are situated just below and behind the mandibular bone (lower jaw) on each side. It supplies major part of the saliva required by our body. It secretes saliva in enormous quantity of both mucous and serous types.

Sub-lingual glands - are the small glands situated on the floor of the mouth on each side (front part of lower jaw). It secretes saliva mostly of mucous type.

These salivary glands have acini as secretory cells and ducts as outlets. The collecting ducts collect the saliva produced and pour them into the mouth on a continuous basis or more when required. Parotid glands have an open duct just opposite the upper second molar tooth whereas sub-mandibular glands and sub-lingual glands open on the floor of the mouth.

Saliva problems commonly arise from infection, inflammation and stone formations in these salivary glands.

(To be continued)