Saliva

Synonyms

spit, saliva

Introduction

Saliva is an exocrine secretion that is produced in the salivary glands located in the oral cavity. In humans, there are three large salivary glands and a large number of small salivary glands. Large salivary glands include the parotid gland (Glandula parotis), the mandibular gland (Glandula submandibularis) and the sublingual gland (Glandula sublingualis).

Together, these are responsible for about 90% of the saliva produced, the rest is provided by the small salivary glands in the oral mucosa. On average, a person produces about 500 to 1500 milliliters of saliva per day, depending, among other things, on how much and what kind of food he or she eats. Even without any food intake, however, a certain amount of saliva is produced, namely about 500 milliliters, which is called basal secretion.

Components and condition

Depending on the nature of the saliva, there are two different types: there is mucinous (or mucous) saliva and serous saliva. Mucinous saliva is rather mucilaginous to viscous. It is produced more often when the influence of the sympathetic part of the autonomic nervous system predominates.

If, on the other hand, the parasympathetic part of the autonomic nervous system predominates, the saliva is rather thin to watery and better suited for digestion. The type of secretion varies depending on the gland, but since all of them ultimately lead to the oral cavity, there is a mixture of the two types of saliva. The main component of saliva is water, of which it consists of 99%.

However, it is the small remaining percentage that ensures that the saliva can perform its functions. Most of the ingredients of saliva are proteins. Particularly important is mucin, a mucus substance that helps to protect the mucous membrane from external mechanical, chemical or physical stimuli.

This substance also helps to give the saliva its special consistency and makes the chyme glide. Among the other proteins, there are, for example, those that participate in the digestive process (amylases, ptyalin) and also important components of the defense system, namely, above all, antibodies of the IgA class. In addition, saliva also contains many small-molecular components, including a large number of electrolytes (the most important are sodium, potassium, calcium and chloride ions), ammonia, uric acid and urea. At rest, the pH of saliva is normally 6.0 to 6.9, but as secretion increases, the pH rises to 7.2, because the faster saliva flow means that there is less time to reabsorb sodium ions from the saliva, which means that a greater number of these ions remain in the saliva, raising the pH.