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THE DIGESTIVE SYSTEM
The digestive system has 3 main functions. First, it breaks down food into smaller
nutrients that the body can use. Secondly, these nutrients are absorbed into the blood.
Thirdly, waste products are eliminated from the body.
The process where the body breaks down food into smaller nutrient molecules is called
digestion. There are 2 types of digestion: mechanical and chemical digestion. In
mechanical digestion, food is physically broken down into smaller pieces by tearing, slicing,
churning and mixing. In chemical digestion, chemicals produced by the body break down
food into very small pieces.
The process of digestion is as follows.
1. The Mouth
The mouth breaks down food by both mechanical and chemical
digestion. Your teeth carry out mechanical digestion. The fluid in your mouth
is called saliva. Saliva plays an important role in chemical digestion. As the
teeth break food into smaller pieces, saliva mixes with the food. Chemicals
called enzymes, found in saliva, break down food into smaller pieces.
2. Epiglottis and Esophagus
When you swallow, muscles in your throat move the food downward. As
this happens, a small flap of tissue called the epiglottis closes off your windpipe
so that food doesn’t enter your lungs, which would cause you to choke.
The epiglottis directs the food into the esophagus, a muscular tube that connects the
mouth to the stomach. The esophagus is lines with mucus. Mucus is a thick, slippery
substance that makes food easier to swallow. Food stays in the esophagus for only about 10
seconds. The muscles surrounding the esophagus contract to push food toward the stomach in
waves. These waves of muscle contractions are called peristalsis.
3. The Stomach
Food leaves the esophagus and enters the stomach. The stomach is a
J-shaped muscular pouch located in the middle of the abdomen. Most
mechanical and some chemical digestion occur in the stomach. Mechanical
digestion occurs as layers of muscle in the stomach lining contract to
produce a mixing and churning motion. Chemical digestion is carried out by
stomach juices that contain enzymes and hydrochloric acid. When the
food has been turned into liquid form, it moves onto the small intestine.
4. The Small Intestine
The small intestine (also called the gut) is the part of the digestive system
where most chemical digestion takes place. Almost all the digestion and
absorption of nutrients occurs here. Enzymes produced by the small intestine,
liver and pancreas contribute to the chemical digestion of food.
