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The Digestive System

In 1822, a man named Alexis St. Martin was wounded in the stomach. Dr William Beaumont

saved St. Martin’s life. The wound, however, left an opening in St. Martin’s stomach that never

healed completely. Beaumont realized that by looking through the opening in St. Martin’s abdomen,

he could observe what was happening inside the stomach. Beaumont observed that food changed

chemically inside the stomach. He hypothesized that chemical reactions in the stomach broke down

foods into smaller particles. Beaumont removed liquid from St. Martin’s stomach and analyzed it.

The stomach liquid contained an acid that played a role in the breakdown of foods into simpler

substances.

Beaumont’s observation helped scientists understand the role of the stomach in the digestive

system. The digestive system has three main functions: to break down food into molecules the body

can use, to absorb these food molecules into the blood so that it can be carried throughout the

body, and to help eliminate waste from the body.

Your body is like a car; without fuel, the car cannot go very far. Your body needs fuel to

function properly. It gets this fuel from the foods that you eat. Humans are classified as

consumers, that is, we need to eat plants or other animals for our food. From our food, we get

three things: energy to keep us going, materials to build our bodies, and materials to rebuild or

replace parts of our bodies (such as skin and blood).

The process by which our food is broken down into smaller, usable parts that our cells can use

is called digestion. The system that digests our food is the digestive system. Our digestive

system is made up of five connected organs commonly known as the digestive tract (or

gastrointestinal tract). Your digestive tract is over 30 feet long! The process of digestion can be

referred to as either being mechanical digestion (physically breaking food into smaller parts) or

chemical digestion (using chemical to break food molecules into smaller chemical building blocks).

Digestion begins in the mouth. Both

mechanical and chemical digestion occurs here. In

your mouth you have teeth to chew and

mechanically break down food, and a tongue to move

the food around and enjoy the flavor. Along with

your teeth and tongue, you have salivary glands

under your tongue. They make saliva, a watery fluid

that helps to moisten the food you are eating,

making it softer and easier to swallow. Your saliva

salivary amylase

contains enzymes called

that help

to begin chemically breaking down your food into

simpler starches or sugars. You can produce as

much as two to three pints of saliva every day!

Once you swallow the food from the mouth, it enters a muscular tube called the esophagus.

Wells 2006

The Digestive System