What is the cause of overactive salivary glands?
Salivary grands overact for meany reasons.
In human being there are three pairs of salivary glands. Largest gland is parotid gland located in wall of the cheek. The moment food is in mouth salivary gland secretes saliva.
Saliva makes food dissolved in saliva. It acts as wetting agent. The mucin of saliva binds the food particles and forms it into a bolus. Dissolved food reaches the taste buds. If food is not dissolved taste buds are unable to sense taste.
The role of salivary amylase on starch is minor. Because when food passes esophagus action of amylase ceases. When mouth is dry in some diseases there is loss of appetite.
Thinking of food also makes secretion of saliva.