Saliva consists of two fluids, mucous and serous. Mucous (slime) is a saccharide glycoprotein called mucin. With water it makes the slippery lubricant used in many parts of the body, where it lines the moving parts, surfaces and tubes. Here it lubricates the mouth, throat and alimentary canal. The serous fluid contains the enzyme amylase which acts in the digestion of carbohydrates. Minor salivary glands on the tongue secrete the amylase. The parotid gland produces purely serous saliva. The other major salivary glands produce mixed (serous and mucus) saliva.
Depending on the types of cells present, the glands may be specific, giving off only one of these two substances; or they may be mixed, giving off combinations of both secretions. Secretions can be increased by the presence, thought, or smell of food and also by thermal stimulation.
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