The Digestive System

Lesson Plan - Get It!

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Your body processes food so you are able to carry out processes like learning, exercise, and growth.

Your favorite food has some combination of nutrients that your body needs. Your favorite food is broken down by the digestive system. Your digestive system starts with your mouth because that is where food enters the body.

Before digesting this lesson, if you missed or need a second helping of any The Human Body lessons, order them in the right-hand sidebar under Related Lessons.

While you may think 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 or a cheeseburger.

• Does your mouth start to water?

That is saliva forming! Saliva is a fluid in your mouth that helps break down chemicals and nutrients 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. The esophagus is a long muscular tube that contracts to move food inside the body.

The esophagus moves food from the mouth to the stomach. At the top of the esophagus is the epiglottis. This is a small flap that prevents food from sliding down the back of the throat into the windpipe.

• Have you ever had food go down the wrong way?

This occurs when food enters the windpipe, and can be very uncomfortable. You will start coughing immediately to bring the food back up.

Once food is pushed down through the esophagus, it arrives at the stomach. This is a muscular organ that stretches to store food, breaks down food into liquid, and releases the nutrient-rich 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 stomach muscles to churn the mixture together. These stomach juices are very strong and damaging.

The stomach is actually lined with a thick, mucus-like substance to prevent damage to the stomach wall. Stomach ulcers — sores inside the stomach — can occur when the stomach acids eat through the mucus protection.

The stomach empties out into the small intestine.

This folded-up, tube-like structure is found under your stomach and may be up to 22 feet long! It isn't very wide — only about two inches around — but the small intestine has a really important purpose!

Your small intestine is responsible for breaking down the liquid nutrients produced by the stomach into substances like vitamins, proteins, minerals, and fats.

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

Once through the small intestine, 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 four inches. It is coiled around the small intestine and measures approximately five feet long, so it's only about one-quarter of the small intestine's length.

As food moves through the large intestine, water is removed and taken in 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 body part has a specific job.

Saliva helps soften the food for digestion as it is pushed through the esophagus. The stomach uses acids to break down the food 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 wasn't able to move through the digestive system in this order?
• What if an individual was unable to process nutrients or water in the intestines?

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