Transcript mechanical and chemical digestion

A Tour
Through the
Digestive
System
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
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.
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
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.

THINK! – Mechanical or Chemical
Digestion?

Both mechanical and chemical digestion
turn your food into an acidic liquid called
chyme.
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.
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.
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.
How Long
Does Digestion
Esophagus?
Take?
4-8sec
Stomach?
2-4hr
Small Intestine?
3-5hr
Large Intestine?
hr-days
Activity: Color Code the Digestive System
mouth
Teeth
Salivary Glands
Esophagus
Liver
Gallbladder
Large Intestine
Small Intestine
Rectum
Stomach
Pancreas