The Digestive Process Begins
In June of 1822, nineteen-year-old Alexis St. Martin was wounded
in the stomach while hunting. William Beaumont, a doctor with
the United States Army, saved St. Martin’s life. However, the
wound left an opening in St. Martin’s stomach that never closed
completely. Beaumont realized that by looking through the
opening, he could observe what was happening inside St. Martin’s
stomach.
Beaumont observed that milk changed chemically inside the
stomach. He hypothesized that chemical reactions inside the stomach broke down foods into smaller particles.
To test his hypothesis, Beaumont removed liquid from St. Martin’s stomach. He had the liquid analyzed to
determine what materials it contained. The stomach liquid contained an acid that could break down foods into
simpler substances.
Functions of the Digestive System
Beaumont’s observations helped scientists understand the role of the stomach in the digestive system. The
digestive system has three main functions. First, it breaks down food into molecules the body can use. Then,
the molecules are absorbed into the blood and carried throughout the body. Finally, wastes are
eliminated from the body.
The process by which your body breaks down food into small nutrient molecules is called digestion. There are
two kinds of digestion—mechanical and chemical. In mechanical digestion, foods are physically broken down
into smaller pieces. Mechanical digestion occurs when you bite into a sandwich and chew it into small pieces.
In chemical digestion, chemicals produced by the body break
foods into their smaller chemical building blocks. For example,
the starch in bread is broken down into individual sugar
molecules.
After your food is digested, the molecules are ready to be
transported throughout your body. Absorption is the process by
which nutrient molecules pass through the wall of your digestive
system into your blood. Materials that are not absorbed, such as
fiber, are eliminated from the body as wastes.
The digestive system is about nine meters long from beginning to
end. As food moves through the digestive system, the processes of
digestion, absorption, and elimination occur one after the other in
an efficient, continuous process.
The Mouth
Have you ever walked past a bakery or restaurant and noticed your mouth watering? Smelling or even just
thinking about food when you’re hungry is enough to start your mouth watering. This response isn’t accidental.
