CHAPTER 8 LESSON 1
How Do Body Cells Get Energy From Food?
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.
Digestion begins inside your mouth
•
•
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.
The Esophagus
•
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.
BEGINS IN THE MOUTH
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.
THE SMALL INTESTINE
•
Peristalsis squirts chyme from the stomach into the small intestine.
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The small intestine is a coiled tube that is about 4 to 7 meters long.
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This is where most digestion takes place.
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The liver makes a fluid called bile.
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Bile breaks apart fat molecules. The gallbladder stores the bile.
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The bile enters the small intestine through a tube called a bile duct.
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The pancreas is a gland that secretes enzymes that complete the digestion of carbohydrates,
proteins, and fats.
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Then food molecules are ready to be absorbed by body cells.
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They are absorbed though tiny, fingerlike structures called villi.
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Thousands of villi line the small intestine
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Blood carries the food molecules to cells all through the body.
THE LARGE INTESTINE
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Peristalsis moves material that cannot be digested to the large intestine.
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The main function of the large intestine is to remove water from undigested material.
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The water is returned to the body.
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The undigested material forms a solid mass called feces.
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Feces are stored in the rectum for a short time.
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The rectum is the last part of the large intestine.
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Smooth muscles line the large intestine.
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They contract and push the feces out of the body though an opening called the anus.
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The journey of food through your digestive system takes about 24 to 33 hours.
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