As the Stomach Churns
Materials
flour paste
food coloring
sealable bags - 1 quart
vegetable oil
scissors (optional)
liquid detergent
coffee filter
funnel and bowl
Introduction
Proper digestion of our food requires mechanical disruption of the food as well
as chemical digestion. The stomach functions in both of these areas. First, the
stomach is highly muscular, and while and after we eat, regular muscle
contractions knead our food and help break up larger pieces which have
escaped our teeth. Second, the stomach releases large amounts of acid, to aid
in chemical digestion. The contractions help to mix the acid thoroughly with the
food. This activity will simulate this process.
Objectives
By performing this activity, students will:

Construct a model of the main digestive organs demonstrating the
role of digestive secretions.

Demonstrate an understanding of the role that dietary composition
plays in digestion.
Procedure
1. Make a thick paste of flour and water in a bowl. This mess will simulate
chewed food in the stomach.
2. Turn down the rim of a sealable bag and pour in several tablespoons of oil,
representing fat consumed in a meal. Add about 1 cup of the flour paste to the
bag. Add 5 or 6 drops of food color, representing stomach acids and enzymes, to
the paste.
2. Seal the bag carefully, removing most of the air. Knead the bag with your
fingers to mix the ingredients. This simulates the contractions of the stomach,
which help disperse the stomach secretions into the food. Continue kneading
until the food color is well mixed with the paste. Notice that the oil does not mix
into the paste, and in fact, rises to the top. This is what happens in the stomach
itself.
3. Now to get really gross, turn down the rim of another sealable bag. This will
represent the small intestine. To represent the pyloric valve, cut a small bottom
corner from the bag with the paste. Slowly squeeze the contents of the stomach
bag into the small intestine bag.
4. Add about a tablespoon of detergent, representing bile, to the small intestine
bag and seal carefully. Knead the bag to mix the contents well. Notice what
happens to the oil now.
5. To simulate the action of the large intestine, transfer most of the contents of
the small intestine bag to a coffee filter suspended over a bowl. The filter will
absorb much of the water and some of the color of the “digested” mixture.
Observe the consistency of the filter contents over a 24 hour period.
Background
The process of digestion occurs in three stages - mechanical disruption,
chemical digestion, and absorption of nutrients. This lab simulates these phases
using simple ingredients. The stomach is a highly muscular organ which
functions both to secrete acid and certain enzymes into its contents, but also to
mechanically crush and blend food elements. Only fairly small pieces of food can
pass through the pyloric valve into the small intestine. Carbohydrate digestion
starts in the mouth with salivary amylase, protein digestion begins in the stomach
with pepsin and acid, but lipid digestion does not begin until the small intestine.
Fats are emulsified there in the presence of bile released by the gall bladder.
Most digestion and absorption of nutrients is completed in the small intestine.
The remaining food debris is passed to the large intestine, which absorbs most
of the water from its contents, and helps to form solid feces.
EXTRA INFORMATION
What is digestion?
Digestion is the process of altering the chemical and
physical composition of food for absorption and then use by
the body cells. This process depends upon endocrine and
exocrine secretions as well as the controlled movement of
ingested food materials along the digestive tract.
Digestive Processes
A) Ingestion occurs when materials enter the digestive tract
by the mouth.
B) Mechanical processing begins with the chewing and
mastication by the teeth and tongue. It continues all along
the digestive tract by the involuntary muscle contractions of
the smooth muscle lining the stomach walls and intestines.
C) Chemical digestion is the breakdown of food into small
organic fragments suitable for absorption by the digestive
epithelium. It starts in the mouth where saliva containing
certain enzymes begin to break down carbohydrates and
continues in the stomach and intestines as other enzymes
and acid is released as the food progresses through the
digestive tract.
D) Absorption takes place mainly in the small intestines,
though important nutrients and water are absorbed by the
large intestine.
E) Compaction is the job of the large intestines. This makes
the feces ready for elimination.
Components of the Digestive System
* Oral cavity {Mouth} - Mechanical Processing, moistening,
mixing with salivary secretions. Mechanically breaks down
food, Moistens food, starts the break down of starch,
glycogen.
* Salivary Glands - Secretion of lubricating fluid containing
enzymes that breakdown carbohydrates.
* Esophagus - Transport of material to the stomach.
* Liver - Secretion of bile (important for lipid digestion),
storage of nutrients and vitamins, many other vital functions.
{Buffering action neutralizes HCL entering small intestine
from the stomach.}
* Gallbladder - Storage and concentration of bile (from liver).
* Stomach - chemical breakdown of material through acid
and enzymatic attack.
* Pancreas - Exocrine cells secrete buffers and digestive
enzymes. Endocrine cells secrete hormones.
* Small Intestine - Provides suitable environment for
enzymatic digestion and absorption of nutrients, vitamins,
and ions. There, the break down of major food molecules
takes place, lubrication of the food pathway is provided, and
control of the acidity of the food released into the small
intestines by the stomach is controlled.
* Large Intestine - Dehydration and Compaction of
indigestible materials to preparation for materials for
elimination.
* Rectum - storage of wastes. Distension (stretching of the
rectum) triggers the defecation reflex that rids the body of
undigested and unabsorbed residues.
Student Worksheet