1. Lesson 1: The digestive system
Chapter 8
Lesson 1: The digestive system

2. I can’t fit that pizza into my cell! Help!
Digestion:
Your digestive system breaks down food for your body to use.
Food contains energy
Food is too large to enter cells  it must be broken down into smaller pieces.
Food must be digested.
Food contains: carbohydrates, fats, and proteins.
Digestion releases energy from food for your cells to use.

3. MMMMMMM……Yummy food! Digestion begins inside your mouth:
Your teeth and jaws chew and crush food while your tongue turns the food over.
Mechanical digestion makes food smaller.

4. Still in the mouth
Salivary glands release saliva (contains digestive enzymes)
Chemical digestion
Enzyme = protein that causes chemical changes (speeds up reactions)
Enzymes in saliva break down carbohydrates into sugars.
Different enzymes work in different areas of the digestive system

5. The esophagus:
When you swallow, the food moves from your mouth into your pharynx (throat).
From the pharynx, it enters the esophagus.
Long tube that connects the mouth to the stomach.
Smooth muscles contract, or squeeze together.
Pushes food down toward the stomach.
Peristalsis = the muscle movement that moves food through digestive system.

6. The stomach:
Food enters the stomach where strong muscles of the stomach walls contract.
Churns and mixes food
Digestive juices are secreted into the mixed food
Hydrochloric acid and digestive enzymes
Special lining protects stomach from acids
Large molecules of food are broken down further until it becomes a liquid
Chyme = liquefied food that exits the stomach

7. The small intestine:
A coiled tube that is about 4-7 m (13-23 feet) long
Most digestion occurs here
Organs and glands help digestion:
Liver: makes bile that breaks apart fat molecules
Gallbladder: stores bile.
Bile enters small intestine via bile duct.
Pancreas: gland that secretes enzymes that digest carbohydrates, proteins and fats.

8. Absorption of food…..finally!
Food molecules are now small enough to be absorbed by small intestine to be taken to your cells.
Finger-like structures called villi line the small intestine.
Increase surface area so more can be absorbed into the blood vessels of the villi.
Blood carries food to your cells.

9. Wait! I can’t do anything with that!
The large intestine:
Some material cannot be digested. It is sent to the large intestine by peristalsis.
Main function: Remove water from undigested material
Water is returned to the body.

10. It’s like putting out the trash.
Undigested material forms a solid mass called feces.
Stored in rectum for a short time.
Smooth muscles contract and push feces out of the body through an opening called the anus.

11. From start to finish
The complete journey of food through the digestive system takes about 24 to 33 hours.