BODY SYSTEMS OTHER THAN SKELETAL
Section I. THE DIGESTIVE SYSTEM
a. The digestive system receives complex food compounds and, by mechanical
and chemical action, splits these compounds into simple molecules that diffuse through
the wall of the intestine into the bloodstream. The mechanical forces involved are
mastication (chewing), local rhythmical movements, and peristalsis (waves of
contraction). The chemical action is very complex. Enzymes (organic compounds that
aid chemical reactions without themselves being utilized) play an outstanding role in
digestion. Certain acids and salts also play vital roles.
b. The digestive system (figure 3-1) consists of the alimentary tract or canal
which extends from the mouth to the anus and the accessory organs of digestion: the
liver, gallbladder, pancreas, and salivary glands. The alimentary tract consists of the
mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.
The mouth, in which the food is masticated and mixed with saliva into a bolus, is
the first division of the alimentary tract. It is divided into the vestibule and the oral
cavity. The vestibule is the space between the teeth and the mucous membrane of the
cheeks and the lips. The oral cavity (figure 3-2) lies within the dental arches and below
the palate. Portions of the maxillary and palatine bones form the hard palate. The soft
palate is a movable fold attached to the back of the hard palate and the sides of the
mouth. In swallowing, the soft palate is raised, isolating the nasopharynx.
The tongue is a freely movable muscular organ intimately associated with the
functions of taste, speech, mastication, salivation, and deglutition (swallowing). It is in
the floor of the oral cavity (figure 3-2) with its base directed backward and its apex