The mouth, or oral cavity, is the beginning of the digestive tract. Here food taken
into the body is broken into small particles and mixed with saliva so that it can be
(1) A person develops two sets of teeth during his life, a deciduous (or
temporary) set and a permanent set. There are 20 deciduous teeth and these erupt
during the first 3 years of life. They are replaced during the period between the 6th and
14th years by permanent teeth. There are 32 permanent teeth in the normal mouth: 4
incisors, 2 cuspids, 4 bicuspids, and 6 molars in each jaw. Each tooth is divided into
two main parts: the crown, that part which is visible above the gums; and the root, that
part which is not visible and which is embedded in the bony structure of the jaw. The
crown of the tooth is protected by enamel. Tooth decay is from the outside in; once the
protective enamel is broken, microorganisms attack the less resistant parts of the tooth.
(2) The primary function of the teeth is to chew or masticate food. The teeth
also help modify sound produced by the larynx to form words.
b. Salivary Glands. These glands are the first accessory organs of digestion.
There are three pairs of salivary glands. They secrete saliva into the mouth through
small ducts. One pair, the parotid glands, is located at the side of the face below and in
front of the ears. The second pair, the submandibular glands, lies on either side of the
mandible. The third pair, the sublingual glands, lies just below the mucous membrane
in the floor of the mouth. The flow of saliva is begun in several ways. Placing food in
the mouth affects the nerve endings there. These nerve endings stimulate cells of the
glands to excrete a small amount of thick fluid. The sight, thought, or smell of food also
activates the brain and induces a large flow of saliva. About 1,500 ml. of saliva are
secreted daily. The saliva moistens the food, which makes chewing easier. It lubricates
the food mass to aid in the act of swallowing. Saliva contains two enzymes, chemical
ferments, which change foods into simpler elements. The enzymes act upon starches
and break them down into sugars.
c. Tongue. The tongue is a muscular organ attached at the back of the mouth
and projecting upward into the oral cavity. It is utilized for taste, speech, mastication,
salivation, and swallowing.
d. Taste Buds. Located on the tongue and at the back of the mouth are special
clumps of cells known as taste buds. Taste buds are sensitive to substances that are
sweet, sour, bitter, and salty.