Functions of the Digestive System
The digestive system includes the digestive tract and its
accessory organs, which process food into molecules that can
be absorbed and utilized by the cells of the body. Food is
broken down, bit by bit, until the molecules are small enough
to be absorbed and the waste products are eliminated. The
digestive tract, also called the alimentary canal or
gastrointestinal (GI) tract, consists of a long continuous tube
that extends from the mouth to the anus. It includes the mouth, pharynx, esophagus,
stomach, small intestine, and large intestine. The tongue and teeth are accessory
structures located in the mouth. The salivary glands, liver, gallbladder, and pancreas are
major accessory organs that have a role in digestion. These organs secrete fluids into the
Food undergoes three types of processes in the body:
Digestion and absorption occur in the digestive tract. After the nutrients are absorbed,
they are available to all cells in the body and are utilized by the body cells in metabolism.
The digestive system prepares nutrients for utilization by body cells through six
activities, or functions.
. The first activity of the digestive system is to take in food through the mouth.
This process, called ingestion, has to take place before anything else can happen.
. The large pieces of food that are ingested have to be broken into
smaller particles that can be acted upon by various enzymes. This is mechanical
digestion, which begins in the mouth with chewing or mastication and continues with
churning and mixing actions in the stomach.
The complex molecules of
carbohydrates, proteins, and fats are transformed
by chemical digestion into smaller molecules that
can be absorbed and utilized by the cells.
Chemical digestion, through a process called
hydrolysis, uses water and digestive enzymes to
break down the complex molecules. Digestive
enzymes speed up the hydrolysis process, which is
otherwise very slow.
. After ingestion and mastication, the food particles move from the mouth
into the pharynx, then into the esophagus. This movement is deglutition, or swallowing.
Mixing movements occur in the stomach as a result of smooth muscle contraction. These
repetitive contractions usually occur in small segments of the digestive tract and mix the
food particles with enzymes and other fluids. The movements that propel the food