Salivary gland and its various types

June 28, 2018

Introduction

The tissue in our mouth that expels saliva is called salivary gland.
Various glands are responsible for secretion of saliva into the oral cavity.
But the salivary glands are mostly known by the three largest pairs: the parotid, submandibular, and sublingual glands.
They are exocrine glands that produce saliva through a system of ducts.
Salivary glands are classified as serous, mucous or sero-mucous (mixed).
It secretes saliva which is watery, tasteless mixture of salivary and oral-mucous gland secretions.
It helps in lubrication of chewed food, moistening the oral walls, and also contains salts to buffer chemicals in the mouth.
It also has salivary amylase, the enzyme that begins the digestion of carbohydrates.
There are six major salivary glands as well as hundreds of minor salivary glands that secrete more than a liter of saliva daily.

A) Parotid glands (Greek: parotis-near the ear)

Among the three major types, parotid glands are the largest.
They are located in front of the ears, covering the masseter muscle posteriorly.
There are long ducts which arise from the glands that pass forward over the masseter muscles which can be felt as a ridge by moving the tip of a finger up and down over the muscle.
Vestibule is the end point of this duct which is alongside the second upper molar tooth.
These ducts are called Parotid or Stensens’s ducts.
These glands secrete water, salts, salivary amylase.
Mucin is not secreted by this gland like other salivary glands.
Mucus is formed when mucin is dissolved in water.
For this reason, the saliva from parotid is clear and watery.

B) Sub-mandibular glands (Greek: submandibular- under the mandible)

They are located on the medial side of the mandible.
Their size is about the size of the walnut, which is roughly half the size of parotid glands.
Their ducts are called Submandibular or Wharton’s ducts.
These ducts open into a papilla on the floor of the mouth beside the lingual frenulum that is behind the lower incisors.
Water, salts, salivary amylase and mucin are secreted by these glands.
Their secretion is comparatively thicker with less salivary amylase than that of parotid.

C) Sublingual glands (Greek: sublingual- under the tongue)

They are located in the floor of the mouth beneath the tongue.
They are the smallest major salivary glands.
They drain their secretions through a dozen or so small ducts.
They are located on the summit of a fold on either side of the lingual frenulum.
These are the ducts that are just behind the orifice of the submandibular ducts.
Water, salts and mucin are mostly secreted.
Their secretion is the most viscous saliva among the three types of salivary glands.
Mucus content is high and salivary amylase is less.

Composition and functions of saliva

It contains about 99% of water and 1% electrolytes and proteins.
It provides solvent for food in order for tasting and digestive reactions to occur.
It also moistens mouth and helps in speech.
Bicarbonates help in maintaining acidic pH of saliva at 6.35- 6.85.
Chlorides in saliva activate salivary amylase.
Immunoglobulin-A aids in antibacterial system.
Presence of lysozyme helps in destroying bacteria, prevents dental decay and infection of mucus membranes.
A protein mucin helps in forming mucus.
Mucus helps in lubricating food, helps from bolus, aids swallowing, help buffer acids and bases.
Phosphates help maintain pH of saliva.
Salivary amylase catalyzes the breakdown of carbohydrates.
Urea and uric acid are secreted as waste products and have no any digesting function.