- 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.
Salivary gland and its various types