1. A Tour Through the Digestive System

2. Magic School Bus – “What’s For Lunch?”
As you watch this episode, complete your graphic organizer so that you can map the pathway food takes as it is digested.
Magic School Bus: What’s For Lunch?_28min

3. Mouth Mechanical digestion begins in the mouth.
In mechanical digestion, food is physically broken down into smaller pieces.
Your teeth carry out mechanical digestion.
THINK! – What are the four types of teeth?
Incisors, Canines, Premolars, & Molars
In addition to teeth, a fluid called saliva moistens your food.
This begins chemical digestion, whereby chemicals break down food into smaller substances.

4. Esophagus As you swallow your food and it enters your esophagus.
The esophagus is a long muscular tube that attaches your mouth to your stomach.
In order to help the food reach the stomach, smooth muscles contract involuntarily pushing the food downward.
These muscle contractions are known as peristalsis.
View peristalisis in Action!
THINK! – How is food prevented from entering your windpipe when you swallow?
When you swallow, a flap of skin called the epiglottis seals off your windpipe

5. Stomach
In your stomach, mechanical and chemical digestion are occuring.
First, your stomach muscles contract creating a churning motion to break down your food.
THINK! – Mechanical or Chemical Digestion?
Then, your stomach secretes an enzyme called pepsin as well as hydrochloric acid to break down food.
Both mechanical and chemical digestion turn your food into an acidic liquid called chyme.

6. Small Intestine, Liver, and Pancreas
From the stomach, chyme enters a long tube called the small intestine.
Here, digestion is completed and absorption of nutrients takes place.
As food travels through the small intestine it mixes with digestive juices from other organs.
The liver produces bile.
Bile is then stored and released from the gallbladder.
Bile helps to break down fat into smaller droplets.
The pancreas also secretes digestive juices into the small intestine.

7. Check out the Villi of the Small Intestine!
The inner surface lining of the small intestine is covered with finger shaped projections called villi.
Villi have tiny blood vessels running through them.
Nutrients pass into these blood vessels.
The blood stream carries the nutrients to the rest of the body.

8. The Large Intestine, Rectum, & Anus
By the time material reaches the large intestine (a.k.a. the colon) most of the nutrients have been absorbed.
The material entering the large intestine contains water and undigested food such as fiber.
As material moves through the large intestine, water is absorbed into the bloodstream and the remaining solid waste material is readied for elimination.
The large intestine ends in a short tube called the rectum. Here waste material is compressed into solid form called feces and exits through a muscular opening called the anus.

9. How Long Does Digestion Take?
4-8sec
Esophagus?
2-4hr
Stomach?
Small Intestine?
3-5hr
Large Intestine?
hr-days

10. Activity: Color Code the Digestive System
mouth
Teeth
Salivary Glands
Esophagus
Stomach
Liver
Gallbladder
Pancreas
Large Intestine
Small Intestine
Rectum