Next up for our look at human bodies and bodily functions inspired by The Human Body book post, let’s explore the digestive system.

We all need to eat, both to supply energy, and to support growth and maintenance of our bodies. For example, we should eat foods that contain calcium to keep our bones strong. But how does the meal we eat become the building blocks and fuel for our bodies?

The process is called digestion.

Digestive System

You probably already know that certain organs are involved in digestion, like the mouth and stomach. Human biologists group related organs together into what are called “organ systems.” Many of the organs involved in digestion are shown in this illustration.

(Public domain illustration from Wikimedia)

The process all starts with your body sending and receiving signals that you are hungry. Once you begin to eat something, say the piece of pizza above, the food passes into your mouth. The teeth break down the bigger pieces into bits while you chew and at the same time glands make saliva, which starts to change pizza chemically.

The tongue helps you swallow the food. As you swallow, the food passes down the esophagus into the stomach. The stomach is like a big bag that is filled with acids and enzymes that dissolve the food, making it into smaller and smaller units.

Once it has been processed to a certain point, the digested food moves into the small intestine (which starts at the duodenum in the illustration). The pancreas and liver, plus the gallbladder help produce the chemicals that regulate digestion. Inside the small intestine, food finishes changing into tiny enough molecules that they can be absorbed into the blood stream and be carried to the cells where they will be used. The walls of the small intestine are covered with special tiny fingers called “villi.” The villi are really good at moving materials to where they need to go.

Anything that hasn’t been digested becomes waste. The waste moves into the large intestine, which consists of the caecum, colon, and rectum. Any excess water is removed and final processing occurs with the help of bacteria. From there the waste exits the body when you go to the bathroom.

This classic video from Kids Health presents it in a slightly different way.

Where is this series going? Check tomorrow’s post for the answer.



See Teach with Fergy for a way to demonstrate digestion using a plastic baggie and bread. A bit gross, but reinforces the different steps in the process in a memorable way.

For a picture book that gives a good introduction, try The Magic School Bus Inside the Human Body

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