SALIVARY GLANDS: FUNCTIONS, TYPES AND DISEASES - ANATOMY AND PHYSIOLOGY - 2024

The salivary glands are part of the digestive system, being the first glands responsible for secreting a series of substances essential for digestion. Located in the area of ​​the face and neck, the salivary glands are exocrine glands; that is, its secretion is expelled out of the body.

Together with the teeth and tongue, the salivary glands make up the structures responsible for the first stage of digestion, known as "chewing and salivation." Although it is the first of many processes, when it fails, digestion is not carried out properly, which in the end creates problems.

At this point in digestion there are two simultaneous and equally important processes: the mechanical action of the teeth when grinding and grinding food, and the chemical action of saliva which, through an enzyme known as salivary amylase, begins to chemically disintegrate. the food.

For its part, the tongue is responsible for mixing what is eaten with saliva and making everything go through the teeth to be properly crushed is the tongue.

Functions of the salivary glands

The main function of the salivary glands is the production of saliva. Saliva is responsible for the digestion of food in the oral phase of digestion, although it also has other essential functions for good oral health.

Among these functions is the lubrication of the mucous membranes of the oral cavity (tongue, palate, gums, etc.), which must be kept moist in order to avoid injuries and ulcerations.

On the other hand, saliva has certain antiseptic properties that allow control of the type and amount of bacteria that inhabit the mouth.

Types of salivary glands

The salivary glands can be divided into two large groups: the minor salivary glands and the major salivary glands.

The major salivary glands are large glands with a well-known and constant anatomical location, while the minor salivary glands are scattered over the entire oral mucosa.

Minor salivary glands

The minor salivary glands are the equivalent in the mucosa of the oral cavity to the sweat glands of the skin.

They are distributed over the surface of almost the entire oral mucosa (with the exception of the gums and part of the hard palate), and are responsible for the constant secretion of saliva but in limited volume, responsible for lubricating the mucous membranes and covering the teeth when we are not eating.

According to their location, which is not usually constant, they can be classified as palatal, lingual, genian, labial and vestibular.

Major salivary glands

The major salivary glands are those that come into action when we begin to eat.

Thanks to a highly complex reflex, an electrical signal is generated even before food enters the mouth that stimulates the secretion of large amounts of saliva (cephalic phase of digestion).

The purpose of this saliva is to help break down large food molecules into smaller fractions that will be easier to absorb later in the digestion process.

From largest to smallest (in volume and importance) the major salivary glands are: parotid, submandibular and sublingual. They are all pairs and are located on each side of the mouth, making a total of six: 2 parotid, 2 submandibular and 2 sublingual.

- Parotid

The parotid is the largest of the salivary glands. It is located in the parotid cell, located in the posterior part of the mouth and in the anterolateral region of the neck in direct relation to the ascending ramus of the mandible.

It is the largest of the major salivary glands and is responsible for the secretion of the greatest amount of saliva (between 1 and 1.5 liters / day), its secretion being predominantly serous.

In addition, the parotid is well known because it is the seat of a relatively common viral infection among children that causes inflammation of the gland or parotitis.

- Submandibular (or submaxillary) gland

It's second on the list when it comes to size. Its size is substantially smaller and it is located on the floor of the mouth, in close relationship with the horizontal branch of the mandible.

Its secretion differs from the parotid gland in that it is a sero-mucinous fluid.

- Sublingual gland

It is the smallest of the major salivary glands and is located immediately below the mucosa that lines the base of the tongue, specifically in the alveolus-lingual groove.

Its secretion is similar to that of the submaxillary gland, although the volume is considerably less due to its size.

Histology

The salivary glands are mixed glands that at the microscopic level present tubules and acini, which is why they are usually classified as tubulo-acinous.

According to the predominant cell type, the salivary glands are classified as serous, mucous and mixed.

Salivary glands whose cells are predominantly serous are responsible for secreting a more crystalline and fluid saliva, rich in ptyalin (a digestive enzyme), while those in which mucous cells predominate tend to secrete denser saliva, rich in mucin.

Finally, when the gland constitution is mixed, the characteristics of saliva depend on the serous-mucosal ratio of the tubulo-acinar cells.

Salivary gland diseases

The salivary glands, like any other structure in the body, are susceptible to various types of diseases, both benign and malignant.

Although the variety of diseases of the salivary glands is very wide, the three most frequent health problems that affect them are infections, lithiasis and tumors.

Infection

The most frequent and common infection of the salivary glands is mumps. It usually affects the parotid glands bilaterally, causing inflammation, pain, and fever that last three to seven days.

It is a viral infection for which the mumps virus is responsible, being more frequent during childhood. This infection does not have specific treatment since it is a self-limited disease (it subsides without treatment); supportive treatment is simply given to relieve symptoms.

Although a few decades ago it was a very common infection, today cases of mumps are less and less due to the development of a very effective vaccine. This scarcity of cases is observed especially in countries where vaccination coverage is extensive.

Salivary lithiasis

Lithiasis or stones are usually associated with the urinary tract (renal lithiasis) and the bile duct (gallbladder and bile ducts). However, as with any gland that secretes a mixture of water and solid compounds, saliva is prone to generating stones under the conditions.

When this occurs, we speak of salivary lithiasis or sialolithiasis, which is nothing more than the formation of small stones inside the gland that eventually migrate through the excretory duct of this gland.

Although it is an asymptomatic entity, once the sialolith (technical name for salivary stone) migrates through the excretory duct, there is a high probability that it will become blocked. This is when symptoms appear.

These are generally characterized by pain, swelling of the affected gland, and inflammation of the area. Depending on the size of the stone and its location, different treatments can be carried out aimed at removing the stone.

Tumors

Salivary gland tumors are usually benign. The most common is the pleomorphic adenoma of the parotid. However, as in any other gland, the salivary glands can be the seat of malignant tumors of the adenocarcinoma type, which are tumors that form in the glandular epithelium.

In both cases, the initial treatment is surgery. However, its extension varies depending on the malignancy of the tumor, as well as the need for complementary surgery and regional lymph node dissection.

For very aggressive and extensive malignant salivary gland tumors, radiation therapy can be used with varying degrees of success.

References

1. Bialek, EJ, Jakubowski, W., Zajkowski, P., Szopinski, KT, & Osmolski, A. (2006). US of the major salivary glands: anatomy and spatial relationships, pathologic conditions, and pitfalls. Radiographics, 26 (3), 745-763.
2. Roberts, WR, & Addy, M. (1981). Comparison of the in vivo and in vitro antibacterial properties of antiseptic mouthrinses containing chlorhexidine, alexidine, cetyl pyridinium chloride and hexetidine. Journal of Clinical Periodontology, 8 (4), 295-310.
3. Scott, J. (1977). Quantitative age changes in the histological structure of human submandibular salivary glands. Archives of oral biology, 22 (3), 221-227.
4. Bigler, JA (1956). Salivary gland infection. Pediatric clinics of North America, 3 (4), 933-942.
5. Levy, DM, Remine, WH, & Devine, KD (1962). Salivary gland calculated. Jama, 181, 1115-1119.
6. Spiro, RH, & Dubner, S. (1990). Salivary gland tumors. Current opinion in oncology, 2 (3), 589-595.
7. Hocwald, E., Korkmaz, H., Yoo, GH, Adsay, V., Shibuya, TY, Abrams, J., & Jacobs, JR (2001). Prognostic factors in major salivary gland cancer.