What Are the Main Functions of Saliva?

Saliva is a clear liquid secreted into the mouth by several salivary glands. The average person produces between 0.5 to 1.5 liters of this fluid daily. Its composition is about 99% water, with a mixture of enzymes, proteins, and minerals foundational to oral and systemic well-being.

The Role in Digestion and Taste

The chemical process of digestion begins in the mouth, thanks to enzymes in saliva. Salivary amylase starts breaking down complex carbohydrates into simpler sugars, while lingual lipase begins the breakdown of fats. This initial step prepares food for more efficient nutrient absorption.

Saliva is also fundamental for taste. For taste buds to detect the chemical properties of food, those chemicals must first be dissolved. Saliva acts as this solvent, allowing dissolved food particles to interact with taste receptors and the brain to perceive distinct flavors.

A protein in saliva known as gustin is involved in the maintenance of taste buds, so a lack of saliva can diminish the ability to taste. The fluid also cleanses the taste buds, preparing them for the next bite and allowing for a clear perception of different flavors.

Oral Health and Protection

Saliva acts as a natural rinsing agent, washing away food particles from between the teeth and oral mucosa. This cleansing action helps reduce the buildup of dental plaque, a sticky film of bacteria that can lead to tooth decay and gum disease.

Saliva’s protective qualities extend to its antimicrobial properties. It contains components that control microbial populations, including enzymes like lysozyme and proteins such as lactoferrin. Saliva also contains antibodies, specifically Immunoglobulin A (IgA), which helps prevent the colonization of pathogenic microorganisms.

Another protective function is saliva’s ability to buffer acids. Acids from plaque bacteria or acidic foods can lower the oral pH. When the pH drops below 5.5, tooth enamel begins to demineralize. Saliva contains bicarbonate that counteracts these acids, maintaining a neutral pH and protecting enamel.

Saliva also facilitates the repair of tooth enamel through remineralization. It is supersaturated with calcium and phosphate, which it deposits onto the tooth surface. This action helps rebuild enamel weakened by acid attacks, repairing the earliest stages of tooth decay. A thin layer of salivary proteins, the acquired pellicle, also forms on teeth to protect them from wear.

Lubrication and Speech

A primary component of saliva’s lubricating quality comes from glycoproteins called mucins, which give saliva its viscous consistency. This allows it to coat oral tissues and bind chewed food into a soft mass known as a bolus. The bolus can then pass smoothly down the esophagus without causing irritation.

This lubricating function is also necessary for clear speech. The moistening of the tongue, lips, and soft tissues allows for the smooth movements required for articulation. Without sufficient salivary lubrication, these tissues can become dry and lead to difficulties in speaking.

Saliva in Bodily Healing and Diagnostics

The oral cavity often heals from injuries like cuts or sores more rapidly than skin, partly due to saliva’s contents. Saliva contains proteins and growth factors, like Epidermal Growth Factor (EGF), that promote tissue regeneration. Proteins called histatins also possess antimicrobial properties and aid in wound closure.

In modern medicine, saliva is a valuable diagnostic fluid because its collection is non-invasive. It can be analyzed to measure hormone levels, such as cortisol to assess stress or melatonin to evaluate sleep cycles. Saliva is also used to detect antibodies against specific viruses, indicating an infection.

The diagnostic utility of saliva extends to genetics, as DNA can be extracted from salivary samples for testing. Additionally, saliva can be screened for therapeutic and illicit drugs. This growing field highlights its role as an indicator of systemic health.