How Do Body Cells Get Energy From Food?

CHAPTER 8 LESSON 1

• 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

• 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.

• 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.

Digestion begins inside your mouth The Esophagus

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.

• 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.

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.

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