Introduction to 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 digestive tract.
Food undergoes three types of processes in the body:
Digestion
Absorption
Elimination
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.
Ingestion
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.
Mechanical Digestion
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.
Chemical Digestion
The complex molecules of carbohydrates, proteins, and fats are
transformed by chemical digestion into smaller molecules that can be
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 digestive tract.
Food undergoes three types of processes in the body:
Digestion
Absorption
Elimination
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.
Ingestion
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.
Mechanical Digestion
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.
Chemical Digestion
The complex molecules of carbohydrates, proteins, and fats are
transformed by chemical digestion into smaller molecules that can be
