Saliva is an important part of the digestive process for many different animals, including humans. Saliva helps moisten food and also starts the digestive process. Saliva is produced by the salivary glands. The Colorado State Pathophysiology Department notes that most animals (including humans) have three different pairs of salivary glands. The parotid glands are located in the cheeks. The submandibular glands can be found in the bottom of the mouth, near the jaw. Finally, there are salivary glands that can be found underneath the tongue, called the sublingual glands.
Saliva is made up of a mixture of water, dissolved substances called electrolytes, enzymes and mucus. As KidsHealth notes, the majority of saliva is water, but the other substances have important roles as well. The enzymes are used to start to break down carbohydrates early in the digestive system. The mucus helps to lubricate the food and make swallowing easier. Saliva also has sodium, potassium and bicarbonate in it. The bicarbonate can be especially important because it can neutralize some of the acid in the stomach.
Saliva Production and Secretion
Saliva production is controlled by the autonomic nervous system, which controls involuntary actions. When the brain is stimulated (such as by the scent of food), it sends signals to the salivary glands. The actual production of the saliva is undertaken by cells called acinar cells. Serous cells make a thin watery form of saliva and mucous cells make a thicker more viscous saliva. The parotid salivary glands are mostly made up of serous cells. The ones under the tongue are mostly mucous cells, with the submandibular representing a mixture of both cell types. When saliva is produced by the acinar cells, it then collects in small ducts, where it can be modified. Small ducts connect to larger ducts, which eventually release saliva into the mouth.