Definition
The oral cavity is lined with different essential glands called oral glands. The most important oral glands are the salivary glands of mammals and poison glands of snakes.
Salivary Glands
These glands are the ectodermal glands derived from the buccal or oral cavity. They secrete saliva which contains
- Watery fluid
- Mixture of water-soluble glycoproteins
- Ptyalin – a starch digesting enzyme
Poison Glands
Poison and other related glands secrete toxins, viscous fluid, or other substances. Histologically they are very much like salivary glands.
Types and locations of Oral Glands
Oral glands are named according to their location of presence
- Labial Glands: Open at the base of lips
- Palatal Glands: Open onto the palate.
- Intermaxillary Glands: these lie between the premaxillary bones.
- Sublingual Glands: These glands lie under the tongue.
- Submandibular Glands: Open on papillae under the tongue.
- Molar Glands: These glands are present near the molar tooth.
- Infraorbital Glands: These are on the floor of the orbit.
- Parotid Glands: These open up into the vestibule opposite one of the upper molars.
Oral Glands in Animal Kingdom
Fishes
Fishes and other aquatic vertebrates lack oral glands as water is available for swallowing and moistening of food. Male catfishes are the only exception among the fishes which have oral glands.
In breeding season, they carry fertilized eggs in epithelial folds in the mouth. These folds also enclose oral glands i.e., goblet cells which produce their secretion in large amounts. After hatching these epithelial folds and oral glands disappear.
Amphibians
In addition to the mucous glands of the tongue, the amphibians have large median intermaxillary glands that lie near the premaxillae. The frog has up to 25 small intermaxillary glands, individually opening up by its own duct and release a sticky secretion on the palate.
Reptiles
Reptiles contain series of small mucous glands lying on the lips, palate, and beneath the tongue. The poisonous snakes have large poison glands which are modified salivary glands and resemble parotid gland – a salivary gland of mammals in histology.
The poison glands open at the base of the maxillary tooth called fang which has a groove for the exudation of poison or toxin. These glands are essential for subduing the prey and they may also be used for defensive purposes.
Heloderma – the only poisonous lizard that possesses sublingual glands which secrete the toxin.
Birds
Aquatic birds almost lack oral glands but all other birds have a series of oral glands (mucous glands). The mucous released may be used for nest-building.
Mammals
There are three different types of salivary glands in mammals:
- Sublingual glands
- Parotid glands
- Submandibular glands
A few mammals such as certain shrews use their salivary glands as poison glands. The parotid gland of mammals is the largest oral gland and ptyalin is always present in its secretions.
Functions of Oral Glands
- These glands perform some important and essential functions
- The secretions release from oral glands is necessary for the proper functioning of the taste buds.
- Viscous secretions make the tongue sticky, such that in frogs for capturing their prey.
- Toxins are used for defensive purposes and to paralyze the prey.