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Lesson Explainer: The Structure and Function of the Digestive System Science

In this explainer, we will learn how to describe the structure and function of the digestive system and explore the main parts of the mouth that aid in digestion.

When you eat your breakfast, where does it go?

It goes on a journey through the digestive system, beginning at the mouth.

The digestive system is a body system.

We have learned that our bodies are made up of body systems, like the nervous system, the circulatory system, and the respiratory system.

Each body system is a group of tissues and organs that work together for a specific function.

We know that the digestive system works to digest and absorb food.

Your breakfast is digested, or broken down, by your digestive system.

Definition: Digestion

Digestion is the process of breaking down food.

Example 1: Identifying the Function of the Digestive System

What does the digestive system do?

  1. It brings oxygen into the body.
  2. It transports oxygen throughout the body.
  3. It allows the body to see, taste, touch, smell, and hear.
  4. It enables us to give birth to new individuals.
  5. It digests and absorbs food.

Answer

Different body systems, like the digestive system, have different functions.

Option A is describing the role of the respiratory system; the respiratory system brings oxygen into the body.

Option B is describing the role of the circulatory system; the circulatory system transports oxygen throughout the body.

Option C is describing the role of the nervous system; the nervous system allows the body to see, taste, touch, smell, and hear.

Option D is describing the role of the reproductive system; the reproductive system enables us to give birth to new individuals.

Option E is describing the role of the digestive system; the digestive system digests and absorbs food.

So, the correct answer is option E: the digestive system digests and absorbs food.

All body systems are made up of organs and tissues.

Let’s take a look at the parts that make up the digestive system.

Many of the parts in the digestive system are part of a long tube called the digestive canal.

Definition: The Digestive Canal

The digestive canal is the long tube in the body that starts at the mouth and ends at the anus, where food is broken down and absorbed for use by the body.

We will classify the parts of the digestive system into two groups:

  1. Parts that are in the digestive canal
  2. Parts that are not in the digestive canal

The parts of the digestive system that are not part of the digestive canal are known as supplementary structures.

Example 2: Identifying Supplementary Structures

Which of these is not part of the digestive canal?

  1. The large intestine
  2. The small intestine
  3. The stomach
  4. The liver

Answer

The digestive canal is the long tube in the body that starts at the mouth and ends at the anus, where food is broken down and absorbed for use by the body.

The stomach, the small intestine, and the large intestine are parts of the digestive canal.

The liver is part of the digestive system, but it is not part of the digestive canal. The liver is a supplementary structure in the digestive system.

So, the correct answer is option D: the liver is not part of the digestive canal.

We can see from the diagram above that the parts are numbered. These numbers tell us the path through which food, like your breakfast, travels through the digestive system.

The mouth has a number 1 beside because it is the first part of the digestive system that food goes through. Food enters the digestive system at the mouth.

Let’s take a closer look at the role of the mouth in digestion.

Different parts of the mouth help with digestion in different ways.

When you bite and chew your food, this breaks it into smaller pieces that are easier to digest and swallow. Teeth break down food by cutting, tearing, and grinding it.

If you look at a set of adult teeth, shown in the figure below, you might notice that they do not all have the same shape.

Here are a set of adult teeth showing the incisors, molars, and canines.

IncisorsCaninesMolars
Incisors are found at the front of the mouth.Canines are found between the incisors and the molars.Molars are found at the back of the mouth.
Adults have 4 in each jaw.Adults have 2 in each jaw.Adults have 10 in each jaw.
They tear and cut food.They tear and cut food.They grind food.

Example 3: Identifying the Structure and Function of Teeth

Here is an image of a mouth. Different types of teeth are shown in different colors.

  1. Which type of teeth is shown in green?
  2. What is the function of these teeth?
    1. Tearing and cutting food
    2. Grinding food

Answer

Part 1

We can see that the teeth shown in green are found at the front of the mouth, and there are 4 of them.

Molars are the large teeth found at the back of the mouth. There are 10 molars in each jaw.

Canines are the teeth found between the incisors and the molars. There are 2 canines in each jaw.

So, the teeth shown in green are the incisors.

Part 2

We know that the incisors and the canines both cut and tear food. The molars at the back of the mouth are larger teeth that grind food.

So, the answer is option A: the teeth in green are the incisors that cut and tear food.

The salivary glands are another part of your mouth that help with the digestion.

The liquid that your mouth produces is called saliva, and it is released from your salivary glands.

Definition: Salivary Glands

The salivary glands are organs in your mouth that secrete saliva. There are three pairs of salivary glands in the mouth.

Saliva is not just water. It contains molecules called digestive enzymes. These help to break down molecules in your food into simpler substances.

For example, starch is a nutrient found in bread. If you chew on bread, the starch will be digested into sugar, which is simpler, by the help of the digestive enzymes found in the saliva.

Definition: Digestive Enzymes

Digestive enzymes are molecules that help to break down food (like starch) into simpler substances (like sugar).

Example 4: Identifying the Role of the Mouth in Digestion

Amer and Dalia are talking about what role the mouth plays in digestion.

Which student is correct?

Answer

We know that the mouth plays a number of different roles in digestion.

Salivary glands are found in the mouth. They secrete a liquid called saliva.

Saliva helps in digestion because it contains enzymes that break down food (like starch) into simpler substances (like sugar).

So, we can see that Amer is correct.

Teeth are found in the mouth. They break down food by cutting, tearing, and grinding it.

Dalia is also correct.

So, both students are correct.

The final part of the mouth that we will learn about is the tongue. Your tongue helps you to taste food and to speak, but it also helps in digestion.

The tongue helps with digestion by

  • pushing food around the mouth,
  • helping to mix food with saliva,
  • helping with swallowing.

Example 5: Identifying the Role of the Tongue

Which of these correctly describes the role of the tongue?

  1. It turns food in the mouth.
  2. It helps us taste food.
  3. It helps mix food with saliva.
  4. All of the answers are correct.

Answer

We know that the tongue is important in more than one way.

It turns food in our mouths, it helps us to taste food, and it also helps to mix food with saliva.

So, the answer is option D: all of the answers are correct.

Let’s recap what we have learned in this explainer.

Key Points

  • Digestion is the process of breaking down food.
  • Digestion begins at the mouth.
  • In each jaw, an adult has
    • 4 incisors and 2 canines at the front that cut and tear food into smaller pieces,
    • 10 molars at the back that grind food.
  • Salivary glands secrete saliva:
    • Digestive enzymes in saliva break down starch into sugar.
  • The tongue
    • pushes food around the mouth,
    • mixes it with saliva,
    • helps with swallowing.

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