Digestive System

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When you start chewing food, a process called digestion begins. The digestive system carries out this process by breaking down food into nutrients that help your body grow, heal, and stay strong.

There are two main steps in digestion: mechanical and chemical breakdown.

First is mechanical digestion. It starts in the mouth through a physical process called chewing, where teeth grind the food into smaller pieces. Here, saliva begins chemical digestion by further breaking down food.

The chewed food then moves down the esophagus, a muscular tube that pushes it into the stomach.

Inside the stomach, the digestion continues, using stomach enzymes to mix with the food and break it into small nutrient molecules.

From there, the food moves into the small intestine, where absorption happens—a process that allows nutrients to be taken up by the blood.

Tiny structures called villi pull nutrients into the bloodstream, where they’re delivered throughout the body.

What’s left passes into the large intestine, where water is absorbed. The remaining waste is formed into solid matter.

Finally, that waste exits the body.

Overview

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Digestive System

The digestive system is how our body turns food into energy and nutrients. It’s made up of a series of connected organs that each have a specific role in the process of digestion. This includes breaking food into smaller parts, absorbing nutrients into the bloodstream, and removing waste. Starting in the mouth and ending in the anus, the system also includes key helper organs like the liver and pancreas. Learning how the digestive system works helps us understand how our bodies grow, heal, and stay healthy.

Science and Engineering Practices (SEP): Developing and Using Models

One way scientists study the digestive system is by creating and analyzing models. These models can be simple diagrams or physical replicas, and they help us see how food moves through each part of the system and how organs interact. Building models allows students to better visualize complex processes, such as how stomach acid breaks down food or how nutrients move into the blood from the small intestine.

Activity Ideas:

Digestive System Mapping – Draw or construct a labeled pathway of the digestive system, showing the organs and the order in which food passes through.
Organ Function Match-Up – Use flashcards to match each digestive organ with its specific function.
Journey of a Sandwich Skit – Act out the journey of food through the digestive system, with students playing the role of different organs and explaining their part.

Crosscutting Concept (CCC): Systems and System Models

The digestive system is a great example of a biological system, a group of parts working together as a whole. Each organ plays a role, and if one part fails, the entire system can be affected. The system starts with ingestion in the mouth, then digestion in the stomach and small intestine, and ends with waste removal in the large intestine. Helper organs like the liver and pancreas release substances that assist in breaking down food.

Examples:

System: Digestive system (organs working together)
Inputs: Food, water
Processes: Mechanical and chemical digestion, nutrient absorption
Outputs: Nutrients for the body, waste products

When we think in terms of systems, we can ask questions like: What happens if the pancreas doesn’t release enzymes? What if the small intestine is damaged? This helps us understand the importance of every part and how they depend on each other.

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