Basics of the Digestive System

Contributor: Hannah Brooks. Lesson ID: 12570

Tasty food goes into your mouth, then later . . . stuff comes out and gets flushed. How and why does food go in one end and out the other? Discover the basics of the amazing human garbage disposal!


Life Science

learning style
personality style
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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  • What happens to the food you put down the garbage disposal in your sink?
  • Are you sure you want to know?

The food disposal in your kitchen works similarly to the digestive system in your body!

Food is taken in and processed by different components until it is removed from the house completely. Your digestive system is similar and starts with your mouth because that is where food enters the body.


While you may think that your mouth is just a smelly place that requires daily brushing, it is actually a key part of the digestive system. Think about what happens when you smell a tasty piece of pizza.

  • Does your mouth start to water?

That is saliva forming! Saliva is a fluid that helps break down chemicals contained in your food. It helps soften the food so you are able to swallow it.

Once the food is swallowed, it enters the esophagus, which connects the throat to the stomach.

esophagus and stomach

The esophagus moves food from the mouth to the stomach through muscle contractions that push the food downward. At the top of the esophagus is the epiglottis, a small covering that prevents food from sliding down the back of the throat into the windpipe.

Once food is pushed down the esophagus, it arrives at the stomach. This is an organ that stretches to store food, break down food into liquid usable nutrients, and release that liquid into the small intestine.

The stomach works like a blender but without the blades! It uses acidic juices to break down solid food and muscles to churn the mixture together. These stomach juices are highly corrosive, or damaging, so it is a good thing the stomach is lined with a protective layer of mucus to prevent damage!


The stomach empties out into the small intestine. This tube is bundled together under your stomach, but it can be about 22 feet long if stretched out.

It isn't very wide, only 2 inches around, but has a really important purpose! Your small intestine is responsible for breaking down the liquid nutrients produced by the stomach into compounds like vitamins, proteins, minerals, and fats.

The small intestine is not able to break down all the nutrients by itself, so it relies on the pancreas, liver, and gallbladder to provide additional juices for digestion.

The pancreas helps the small intestine process fats and proteins, while the liver provides bile to help the body absorb fat. Bile is stored by the gallbladder until the small intestine uses it during digestion.

These three organs play an important part in the digestive system!

digestive system

Once through the small intestine, with the help of additional organs, food is passed to the large intestine.

  • Why do you think it is called the large intestine?

Well, it is double the diameter of the small intestine, around 4 inches! It is coiled around the small intestine and would measure around 5 feet long!

As food moves through the large intestine, water is removed and absorbed by the body. As water is removed, the waste becomes more solidified and is able to be excreted.

The large intestine ends with the rectum. This is where your waste remains until it is time to go to the bathroom. The final stop on the digestive system is passage through the anus into a toilet.


Your digestive system is working to process every bite of food you take in. As food moves through the system, each component has a specific job.

  Saliva helps soften the food for processing as it is pushed through the esophagus.
  The stomach uses harsh chemicals to break food down before moving it into the small intestine.
  In the intestines, nutrients and water are removed for use by the body.
  Waste is finally excreted through the rectum and anus.


  • What would happen if food weren't able to move through the digestive system in this order?
  • What if an individual were unable to process nutrients or water in the intestines?

Write a quick reflection in your notebook.

In the Got It? section, practice identifying components of the digestive system!

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