Salivary gland

The salivary glands produce saliva, which keeps the mouth and other parts of the digestive system moist. It also helps break down carbohydrates (with salivary amylase, formerly known as ptyalin) and lubricates the passage of food down from the oro-pharynx to the esophagus to the stomach.

There are three main pairs of salivary glands: the parotid, the submandibular and the sublingual glands. There are also many small glands in the tongue, cheeks, lips and palate, all of which consist entirely of mucous secreting cells (see Histology below) except for the serous glands of von Ebner, which reside within the moats surrounding the circumvallate papillae in the posterior 1/3 of the tongue, anterior to the terminal sulcus.

Histology

Two types of epithelial cells in salivary glands produce either mucous or serous secretions. The parotid gland produces serous secretions. The submandibular and submaxillary glands contain a mixture of both types of cells, and produce a mixture of the two liquids.

Details

Classification

The salivary glands can be classified into serous, mixed and mucous glands.

The only serous gland is the parotid gland. This gland produced serous secretions only; therefore it contains cells called serous acini.
The submandibular glands are denominated as mixed glands, producing mixed secretions that contain both serous and mucous secretory products.Consequently, such glands contain serous acini as well as mucus acini.
The sublingual glands produces mucus secretions. Therefore only containing mucous acini.

Structure

The glands are enclosed in a capsule of connective tissue and internally divided into lobules. Blood vessels and nerves enter the glands at the hilum and gradually branch out into the lobules. There are 3 main types of cells that are found in the major salivary glands:

Serous cells, which are pyramidal in shape and are joined to usually form a spherical mass of cells called acinus, with a small lumen in the centre.
Mucous cells are usually cuboid in shape and organised as tubules, consisting of cylindrical arrays of secretory cells surrounding a lumen. These cells preoduce glycoproteins that are used for moistening and lubricating functions of the saliva.
Myoepithelial cells surround each secretory portion and are able to contract to accelerate secretion of the saliva.

In the duct system, the lumens formed by the secretory cells empty into intercalated ducts, which in turn join to form striated ducts. These drain into ducts situated between the lobes of the gland (called interlobar or excretory ducts). The main duct of the salivary glands ultimately empties into the mouth.

Location of the glands

There are three salivary glands:

The parotid gland is located near the ear (par- = next to, -otid = ear), and is the largest of the salivary glands.
The sublingual gland lies underneath the tongue.
The submandibular gland is a U-shaped structure, and lies beneath the ramus of the mandible (the angle of the chin).

Role in disease

See mumps (parotiditis epidemica) and Sjögren syndrome.

Salivary duct calculus may cause blockage of the ducts, causing pain and swelling of the gland.

Tumors of the salivary glands may occur. These are usually benign, but may be malignant. The most common type of benign tumor is Pleomorphic adenoma, followed by Warthin's tumor. The most common malignant tumor is Mucoepidermoid carcinoma.

Diagnostic investigation

A sialogram is a radiocontrast study of a salivary duct.

External links

Digestive system | Mouth | Glands | Exocrine system

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