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Physiology and Functions of Saliva

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4 min read


Human saliva is not only important for digestion but also necessary for immune defense. Read the article to know all about the significance and functions of saliva.

Medically reviewed by

Dr. Sowmiya D

Published At June 16, 2022
Reviewed AtAugust 7, 2023

What Does the Saliva Contain?

In a normal individual with neither systemic nor oral disease, the salivary glands in a healthy individual secrete approximately 500-1500 ml of saliva daily. The pH of saliva varies around 6-7.4. Saliva is composed of multiple components, but 99 % of this content is water, and the remaining 1% comprises organic substances, L amylase or Ptyalin, lingual lipase, small amounts of urea and uric acid, cholesterol, mucin, lysozymes, inorganic substances like Na+, cl-, K+, HCO3- etc.

In addition to the oral functions of chewing and swallowing, the important physiological role that takes place in the oral cavity is the lubrication of food. Moreover, saliva is an essential oral fluid that contains several immunoglobulins and plays a vital role in immunity. In addition, it possesses a potent antimicrobial activity and a buffering capacity. It also plays a crucial role in the cleansing and lubrication of the mouth and the food intake, along with the primary function of the chemical digestion of polysaccharides obtained through diet.

What Are the Functions of the Salivary Glands?

The saliva is secreted mainly by three pairs of salivary glands. These are also known as major salivary glands. The largest of the major salivary glands is the parotid gland which weighs approximately 20-30 g and is located at the angle of the jaw. The parotid gland is a pure serous gland meaning that its secretion of saliva is more watery and fluid-like in consistency, containing a water content of 90 % or more. This gland is primarily responsible for 25% of the total salivary secretion. The ducts of the parotid gland open into the inner side of the right and left cheek, with the salivary secretions pouring into the oral vestibule. The submandibular salivary gland is the second largest salivary gland located bilaterally, i.e., one on each side around the location of the angle of the mandible. This gland is composed of serous and mucous acini, with the serous acini that are more dominant within the gland structure. In addition, this gland possesses an s-shaped duct that opens a pathway for the secretions into the sublingual papilla and is located lateral to the frenulum lingua near the tongue. The sublingual glands are the smallest of the three major salivary glands that lie below the oral mucosa on the floor of the mouth. This gland contains serous and mucinous acini, with the mucous acini more dominant or predominating. The ducts of the sublingual glands are approximately 8-20 in the count, and they open into the oral cavity through the summit of the sublingual fold (the sublingual fold is the raised mucosal ridge in the gland that starts from the sublingual papilla and runs both laterally and backward). A few ducts of the sublingual gland may also open into the submandibular duct.

What Are the Differences in Salivary Content in Different Salivary Glands?

The important medical fact to note is that both the sublingual and submandibular glands have the salivary secretion with increased concentration of proteins and hence are more viscous compared to the watery or liquid parotid gland secretions of saliva. In addition, several more minor glands secrete saliva throughout the oral cavity.

However, minor salivary glands located in the tongue secrete lipase. The composition of saliva that varies from individual to individual always depends on the salivary flow rate. This secretion is controlled basically by the autonomous nervous system by parasympathetic stimulation. Human saliva in healthy individuals is more watery with minimal enzymatic and organic content. When the sympathetic nervous system stimulates saliva, even small amounts contain rich organic material. As we know, reflex secretions are a significant component of human life as conditioned reflexes like sight, smell, and the thought of food or hunger can stimulate or increase the salivary flow rate.

What Are the Phases of Salivary Secretions?

There are four phases of salivary secretions:

  1. Cephalic phase: in this first phase, even before the entry of food into the mouth, the conditioned reflexes that are sight and smell of food stimulate the salivary secretion.
  2. The buccal phase: It is characterized by the predominance of unconditioned reflexes like the salivary secretion naturally present to lubricate the food in the mouth. The food stimulates the buccal receptors of the oral cavity, called the buccal phase.

  3. Esophageal phase: Though the degree of salivary secretion is lower in this phase, the food eventually enters the esophagus.

  4. Gastric phase: This occurs due to the food being ingested in our stomach that stimulates salivary secretion, though to a lesser degree. Especially when there is gastric irritation or when a person feels nauseating, salivary secretion is increased, which is initiated through the gastric phase.

  5. The intestinal phase: It occurs only when there is irritant material or food within the upper intestine.

What Is the Primary Function of Saliva?

The functions of saliva mainly are 

  • The chemical digestion of polysaccharides, and complex dietary sugars, including starch, are converted to disaccharide maltose by the amylase enzyme. This enzyme acts only at the average concentrations of salivary buffering at a ph of around 5.8-7.4, depending on the individual's salivary flow rate. This enzyme activation is terminated by the consequent acidic content of the gastric juices (1.5-1.8 ph) degrades the enzyme effect.

  • Lubrication of dietary components or starch or food: the high content of the salivary secretions not only prevents the food from drying out and being moistened but is converted into the semi-solid bolus that makes an individual capable of swallowing the food.

  • Nonspecific immune defense: a potent combatant of microbes and the infectious organisms in the oral cavity through lysozymes and immunoglobulins.

  • Cleansing and taste sensations: An adequate salivary flow is necessary to keep the palate and the oral cavity, including the tongue, moist, soft, and smooth, free from any form of abrasiveness to prevent damage to the oral mucous membranes. Though the primary mechanism of the taste receptors is in the tongue, saliva also plays a role in the stimulation of taste receptors in the taste buds of the language.


To conclude, saliva has multiple roles in the human immune system for maintaining oral and systemic health through its contribution to the digestive, lubricating and defensive functionality. It plays a major role in digestion of food also.

Frequently Asked Questions


What Purposes Does Saliva Serve?

Saliva moistens the mouth, lubricates it, and helps in swallowing. It neutralizes harmful acids. Additionally, it disinfects the mouth and stops bad breath, guards against tooth decay and gum disease, preserves enamel, and quickens the healing of wounds. It also serves as a diagnostic tool for certain hereditary and autoimmune diseases, as well as for determining drug doses.


What Regulates Salivation Physiologically?

The salivary secretion is dependent on cholinergic signaling from parasympathetic nerves. Additionally, the secretion of salivary protein content depends on neuropeptide signaling. Secretion of the three primary salivary glands, the parotid, submandibular, and sublingual, is regulated by sympathetic nerves.


What Is the pH of Saliva?

The pH of saliva typically ranges from 6.2 to 7.6, with 6.7 being the average value. The mouth's pH at rest remains above 6.3. Saliva helps to keep the pH of the mouth cavity close to neutral (6.7–7.3).


What Is the Primary Purpose of Saliva?

Saliva's major job is to support healthy oral and digestive systems. It includes enzymes that start the breakdown of food's carbohydrates, such as amylase. Saliva also aids in lubricating and moistening food, which facilitates chewing and swallowing. Additionally, it includes antibacterial substances that support good oral hygiene by limiting the development of potentially hazardous germs in the mouth.


Which Body Part Makes Saliva?

Saliva is produced by the major and minor salivary glands in the oral cavity. The major salivary glands are the parotid gland, the submandibular gland, and the sublingual gland.


What Causes Dry Mouth?

When the salivary glands in the mouth are unable to produce enough saliva to keep the mouth moist, a dry mouth results. It can occur due to certain medications, diseased conditions, or psychological reasons like anxiety and stress.


Is Saliva an Acid or a Base?

The average pH levels of saliva normally range from 6.2 to 7.6, depending on variables including nutrition and individual variance. It helps to maintain the mouth's pH balance, neutralizing the acids that bacteria create and promoting general dental health.


What Components Makeup Saliva?

Many electrolytes, such as sodium, potassium, calcium, magnesium, bicarbonate, and phosphates, can be found in saliva. Moreover, it contains proteins, enzymes, mucins, immunoglobulins, and nitrogenous products, including urea and ammonia.


Which Is the Largest Salivary Gland?

The parotid gland is the body's biggest salivary gland. It starts just behind the bottom portion of the ear and runs down to the jawline. Saliva is produced by the parotid gland and helps in mouth lubrication and digestion.


What Salivary Gland Is the Smallest?

The smallest of the main salivary glands is the sublingual gland. In comparison to the bigger parotid and submandibular glands, it is situated behind the tongue and is in charge of producing a lesser amount of saliva. The sublingual gland, despite its small size, contributes to the preservation of lubrication and moisture in the mouth.


What Is the Site of Digestion of Saliva?

In the mouth, digestion starts with saliva. Salivary enzymes like amylase begin dissolving complicated carbs into less complex sugars like maltose. Carbohydrates are first broken down in the mouth, where saliva is combined with the meal as you chew and swallow it, preparing it for a further breakdown in the stomach and small intestine.


What Are the Different Varieties of Saliva?

The different varieties of saliva are serous (produced by serous cells- parotid gland) and mucous saliva (produced by mucous cells- sublingual gland). Serous saliva is thin and watery and contains zymogens, antibodies, and inorganic ions).


What Volume of Saliva Is Formed per Day?

Saliva production by the human body ranges from 0.5 to 1.5 liters per day on average. Saliva production varies from person to person and can be impacted by things including hydration, food, and general health. In terms of digestion and dental health, saliva is essential.


What Exactly Is Serous Saliva?

Serous saliva is produced by the serous glands. The parotid gland is serous in nature. Serous saliva is rich in zymogens, antibodies, and inorganic ions. They are thin and watery in nature.
Dr. Achanta Krishna Swaroop
Dr. Achanta Krishna Swaroop



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