Digestion
Objectives:
1.
2.
Students will be able to describe the 3 main
functions of the digestive system.
Students will be able to identify the organs of
the digestive system and their functions.
Indian Hills Middle School
Functions of the Digestive
System
The digestive system has 3 main functions:
Digestion
Absorption
Elimination
Digestion
The process by which the digestive system breaks down
food into molecules that the body can use.
There are 2 kinds of digestion:
 Mechanical

Foods are physically
broken into smaller
pieces
 Chemical
 Chemicals produced by
your body break large
molecules into smaller
ones that your body can
use.
Absorption & Elimination
 Process by which nutrients
pass through the lining of
your digestive system into
your blood. The blood then
transports the nutrients
throughout the body.
 Materials that are not
absorbed are eliminated
from the body as wastes.
Structures of the Digestive System:
 The mouth, pharynx, esophagus, stomach, small
intestine, and large intestine.
 The liver, gallbladder, and pancreas all aid in digestion.
MOUTH
 Mechanical digestion occurs in your
mouth as teeth tear and crush and the
tongue moves the food around
 Chemical digestion occurs as an
enzyme in saliva begins to break down
starches in the food.
 Saliva moistens the bites of food into a
slippery mass that can be easily
swallowed.
PHARYNX
o The junction between the digestive
tract and the respiratory system.
 Epiglottis is a flap of tissue that seals
off the windpipe or trachea
preventing food and liquid from
entering your lungs
Structures of the Digestive System
 ESOPHAGUS
A small muscular tube that connects the
pharynx to the stomach.
Muscles contract, peristalsis, and push
the food through the esophagus toward
the stomach.
STOMACH
• Food passes through a valve into the
stomach.
• The stomach can hold 1 gallon of food
or water.
• Mechanical digestion occurs as 3
layers of muscle tissue churn the food.
• Gastric juices
help break down
food creating a
chemical reaction.
• Gastric acid kills
bacteria in food.
• The food has been turned into chyme
and moves into the small intestine.
Structures of the Digestive System
Small Intestines
 Most chemical digestion and
absorption of nutrients takes
place in this 20’ long tube.
 The liver produces bile that
breaks up fat droplets that clump
together.
 The gallbladder is a small storage
space that holds the bile from the
liver.
 The pancreas secretes enzymes
into the small intestine that
breaks down carbs, proteins, &
fat.
Structures of the Digestive System
Small Intestine
Millions of villi found in
the small intestines
absorb nutrient
molecules into the blood
system.
Structures of the Digestive System
The Large Intestine
 When the material reaches the




end of the small intestine, most
nutrients have been absorbed.
It then moves into the large
intestines also called the colon
for about 12-24 hours.
Some absorption takes place
with the remaining water.
Produces vitamins in the large
intestines.
The rectum collects the waste
called feces or stool and
eliminates it through the anus.
Structures of the Digestive System
Can you follow the path of the chicken salad sandwich?
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Healthy Review & Questions
1.
2.
3.
4.
5.
6.
List the three main functions of the digestive
system in the order that they occur.
What is digestion and name the two kinds of
digestion?
Where does digestion begin and what kind of
digestion is it?
What is peristalsis?
What does the stomach do to the food?
What organ absorbs most of the nutrients from the
food into the bloodstream to be used as energy?