(4) Absorption. The taking up of digested food from the digestive tract into
the cardiovascular and lymphatic systems for distribution to the body's cells.
Defecation. The discharge of indigestible substances from the body.
d. Organization of Digestive Organs. The digestive organs are commonly
divided into two main groups: the gastrointestinal (GI) tract (also called the alimentary
canal) and the accessory structures.
(1) The gastrointestinal (GI) tract. The gastrointestinal tract is a continuous
tube which extends from the mouth to the anus and which runs through the ventral body
cavity. The tube is about 30 feet long in a cadaver and a little shorter in a living person
because the tube's wall muscles are toned. From the time food is eaten until it is
digested and eliminated, it is in the gastrointestinal tract. Muscular contractions in the
walls of the GI tract churn the food breaking it into usable molecules. The organs which
make up the gastrointestinal tract are the mouth, pharynx, esophagus, stomach, small
intestine, and large intestine. These organs are sometimes referred to as the primary
organs of the digestive system.
(2) Accessory structures. These structures include the teeth, tongue,
salivary glands, liver, gallbladder, and pancreas. Except for the teeth and the tongue,
all the structures lie outside the continuous tube which is the gastrointestinal tract.
Secretions that aid in the chemical breakdown of food are produced and stored by these
structures. Eventually, such secretions are released into the GI tract through ducts in
(3) General histology (structure of tissues). The gastrointestinal wall has
the same basic tissue arrangement from the mouth to the anus. There are four coats
(also called tunics): the mucosa, submucosa, muscularis, and serosa (adventitia). The
mucosa, the inner tissue layer, contains blood and lymph vessels which carry nutrients
to other tissues and also protects the rest of the body against disease. The submucosa
is made up of loose connective tissue and binds the mucosa to the next layer which is
the muscularis. Skeletal muscle in the muscularis of the mouth, pharynx, and
esophagus produce voluntary swallowing. The outer layer of tissue is the serosa.
Remember that the GI tract carries food which often contains bacteria.
a. The mouth is also referred to as the oral cavity or the buccal cavity. This
organ is formed by the cheeks, the hard palate, the soft palate, and the tongue. The
lips and the teeth are also considered part of the mouth.