1. How Do Body Cells Get Energy From Food?
Chapter 8 Lesson 1
How Do Body Cells Get Energy From Food?

2. Digestion Your digestive system breaks down food for your body to use.
Food contains energy for your body’s cells.
Food is too big to enter cells, so it must be broken down into smaller pieces.
This process is called digestion
Food contains carbohydrates, proteins, and fats.
In digestion, food is broken down into a form that your cells can use for energy.

3. Digestion begins inside your mouth
The Esophagus
Your teeth and jaws chew and crush your food while your tongue turns it over.
As you chew, salivary glands secrete saliva, a fluid that has a digestive enzyme.
An enzyme is a protein that causes chemical changes.
The enzyme in saliva changes carbohydrates into sugars as you chew.
Digestive enzymes help to break down food.
Each part of the digestive system has its own special digestive enzymes.
As you chew, food moves around in your mouth.
When you swallow, the food moves into your pharynx, or throat.
Then it moves into the esophagus.
This long tube connects the mouth to the stomach.
Smooth muscles in the esophagus contract, or squeeze together, to push food toward the stomach.
This movement is called peristalsis.

4. Begins in the mouth

5. The Stomach Strong muscles of the stomach walls contract.
This action churns and mixes the food.
The stomach walls secrete digestive juices.
These juices are hydrochloric acid and digestive enzymes.
A special moist lining protects the stomach from being eaten away by the acids.
The acid and enzymes break down large molecules of food.
Solid food becomes liquid. This liquid is called chyme.

6. The small Intestine
Peristalsis squirts chyme from the stomach into the small intestine.
The small intestine is a coiled tube that is about 4 to 7 meters long.
This is where most digestion takes place.
The liver makes a fluid called bile.
Bile breaks apart fat molecules. The gallbladder stores the bile.
The bile enters the small intestine through a tube called a bile duct.
The pancreas is a gland that secretes enzymes that complete the digestion of carbohydrates, proteins, and fats.
Then food molecules are ready to be absorbed by body cells.
They are absorbed though tiny, fingerlike structures called villi.
Thousands of villi line the small intestine
Blood carries the food molecules to cells all through the body.

7. The large intestine
Peristalsis moves material that cannot be digested to the large intestine.
The main function of the large intestine is to remove water from undigested material.
The water is returned to the body.
The undigested material forms a solid mass called feces.
Feces are stored in the rectum for a short time.
The rectum is the last part of the large intestine.
Smooth muscles line the large intestine.
They contract and push the feces out of the body though an opening called the anus.
The journey of food through your digestive system takes about 24 to 33 hours.

8. Review