Mouth—The first digestive structure:
Mouth prepares the food for digestion. In higher animals, particularly in man, the digestion of nutritive substances of food stuffs begins in the buccal-cavity.
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As soon as the food is entered the mouth, the process of mastication starts with the help of teeth.
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Teeth break the food into smaller particles. During the process of mastication the food is thoroughly mixed with the fluid saliva secreted by the salivary glands.
Salivary glands:
In the buccal cavity of most vertebrates four pairs of salivary glands are found. These are the infra-orbital, parotid, sublingual and submaxillary glands. In humans there are only three pairs, there being no infra-orbitals.
Salivary glands may contain either mucous cells or serous cells. Mucous cells contain large transluscent granules (consisting of a precursor of mucin) and such cells appear pale or translucent in histological sections.
Serous cells contain opaque small zymogen granules (consisting of a precursor of amlase or ptyalin).
Parotid glands:
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These are the largest of the salivary glands, found lying one on each side of the face below and in front of the ears.
The secretion of each parotid gland passes via Stensen’s duct which opens into the mouth opposite the site of the second upper molar tooth.
The disease called mumps is an infection of the parotid glands that causes swelling and irritation.
The parotid glands are purely serous and so they secrete zymogen granules.
Submaxillary glands:
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These glands are found within the angles of the lower jaws. These glands contain both types of cell, but predominantly serous.
Their secretion passes via Wharton’s duct into the floor of the mouth at the side of the frenulum linguae.
Sublingual glands:
These are found embedded in the mucous membrane in the floor of the buccal cavity, under the tongue. Ducts of these glands open into the sublingual part of the mouth under the tongue.