The composition of human saliva: what does this liquid hide in itself?

We swallow saliva regularly. And we are accustomed to the fact that the oral cavity is always wet and we perceive the cessation of sufficient production of this biological fluid with suspicion. As a rule, increased dry mouth is a sign of some disease.

Saliva is a common and necessary biologically active liquid. Helps maintain the level of immune defense in the oral cavity and digestion of food. What is the composition of human saliva, fluid production rates, as well as physical and chemical properties?

A little biology

Saliva is a biological substance secreted by the salivary glands. Liquid is produced by 6 large glands - submandibular, parotid, sublingual - and many small ones located in the oral cavity. Up to 2.5 liters of fluid are released per day.

The composition of the secretions of the salivary glands differs from the composition of the fluid in the oral cavity. This is due to the presence of food debris and the presence of microorganisms.

Functions of biological fluid:

Function [edit]

Further information: Digestion

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The salivary glands produce saliva, which has many benefits for your mouth and overall health. These benefits include:

Protection

Saliva is composed of proteins (such as mucins) that lubricate and protect both the soft and hard tissues of the mouth. Mucins are the main organic constituents of mucus, a mucous viscoelastic material that covers all surfaces of the mucous membrane. [23]

Buffering

In general, the higher the saliva flow rate, the faster the cleansing and the higher the buffer capacity, hence the better protection against caries. Therefore, in individuals with a lower salivary secretion rate combined with a low buffering capacity, salivary protection from microbes is reduced. [24]

Pellicle formation

Saliva forms a film on the surface of the tooth that prevents wear. The film contains mucins and proline-rich glycoprotein from saliva. Proteins (staterin and proline-rich proteins) in the salivary film inhibit demineralization and promote remineralization by attracting calcium ions. [25]

Preserving the integrity of teeth

Demineralization occurs when the enamel is destroyed due to the presence of acid. When this occurs, the buffering effect of saliva (increases the flow rate of saliva) prevents demineralization. Saliva can then help remineralize the tooth, strengthening the enamel with calcium and phosphate minerals. [26]

Antimicrobial action

Thanks to the elements it contains, saliva can prevent the growth of germs. For example, lactoferrin in saliva naturally binds to iron. Since iron is a major component of bacterial cell walls, removing the iron destroys the cell wall, which in turn destroys the bacteria. Antimicrobial peptides such as histatins inhibit the growth of Candida albicans and Streptococcus mutans. Salivary immunoglobulin A serves to aggregate oral bacteria such as S. mutans and prevent plaque formation. [27]

Fabric repair

Saliva can promote soft tissue repair by decreasing clotting time and increasing wound contraction. [28]

Digestion

Saliva contains the enzyme amylase, which hydrolyzes starch to maltose and dextrin. As a result, saliva allows digestion to occur before food reaches the stomach. [29]

Taste [30]

Saliva acts as a solvent in which solid particles can dissolve and enter the taste buds through the oral mucosa located on the tongue. These taste buds are found within the leaf and circumferential papillae, where the minor salivary glands secrete saliva. [31]

Physical properties and composition of saliva

Biological fluid in a healthy person has a number of physical and chemical properties. They are presented in the table.

Table 1. Normal characteristics of saliva.

Index	Characteristic
Transparency	Transparent, minor inclusions of air, pieces of food.
Density	Slightly higher than the density of water, depending on the composition - from 1 to 1.12 g/ml.
Color	Normally – absent.
Viscosity	Insignificant and unstable, depends on the current state of the body.
Taste	Absent.
pH	Alkaline – 7.4–8.0.

The main component of oral fluid is water – up to 98%. The remaining components can be roughly divided into acids, minerals, trace elements, enzymes, metal compounds, and organics.

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Subtleties of saliva secretion

0.5 ml of saliva per minute should be produced in a healthy person during the daytime

The work of the salivary glands is controlled by the autonomic nervous system, centered in the medulla oblongata. Salivary fluid production varies depending on the time of day. At night and during sleep, its amount decreases sharply and increases during the day. In a state of anesthesia, the work of the glands completely stops.

During wakefulness, 0.5 ml of saliva is secreted per minute. If the glands are stimulated - for example, during a meal - they produce up to 2.3 ml of liquid secretion.

The composition of the secretion of each gland is different. When it enters the oral cavity, mixing occurs, and it is called “oral fluid.” Unlike the sterile secretion of the salivary glands, it contains beneficial and opportunistic microflora, metabolic products, desquamated epithelium of the oral cavity, discharge from the maxillary sinuses, sputum, red and white blood cells.

pH values are influenced by compliance with hygiene requirements and the nature of food. So, when stimulating the work of the glands, the indicators shift to the alkaline side, and with a lack of fluid - to the acidic side.

In various pathological processes, there is a decrease or increase in the secretion of oral fluid. Thus, with stomatitis, neuralgia of the branches of the trigeminal nerve, and various bacterial diseases, overproduction is observed. With inflammatory processes in the respiratory system and diabetes mellitus, the secretion production of the salivary glands decreases.

Other animals[edit]

The salivary glands of some species are modified to produce proteins—salivary amylase is found in many, but not all species of birds and mammals (including humans, as noted above). Additionally, the venom glands of venomous snakes, Gila monsters, and some shrews are actually modified salivary glands. [35] In other organisms, such as insects, salivary glands are often used to produce biologically important proteins such as silk or glue, while the salivary glands of flies contain polytene chromosomes, which have been useful in genetic research. [41]