Physiological Modeling of
the Digestive System
http://vubme.vuse.vanderbilt.edu/group29_01/
Submitted by: Lauren Shipp and Megan Davis
April 23, 2002
Advisor: Mel Joesten
Professor: Paul King, Ph.D
BME 273 Senior Design
Vanderbilt University
Department of Biomedical Engineering
ABSTRACT
The purpose of this project was to design a model of the digestive system for
VSVS (Vanderbilt Students Volunteer for Science). This group would use our model in
helping to teach the physiology of the digestive system to children in the 3rd through 8th
grades. The model would be kid-friendly, interactive, and accurately portray the
digestive system at an appropriate educational level. We accomplished this by building a
three dimensional wooden structure of human shape and incorporating life-size organs
using lightweight spackle. A tubing system with working valves was also added to our
model to demonstrate the direction of flow through the digestive tract. Our advisor and
other instructors were consulted to help develop appropriate lesson plans and visual aids
to coordinate with our physical model. These lesson plans and other teaching aids were
designed at two different age levels: third though fifth grade, and sixth though eighth
grade. Future classroom testing of our model later this week will reveal the true success
of our project. From teacher input, previous science models, and past VSVS lesson
plans, it can be concluded that our model was a success and will be used for many years
to come to help children learn about the digestive system.
2
INTRODUCTION
Vanderbilt Students Volunteer for Science (VSVS) is an organization composed
of undergraduates, graduates, and medical students. On a weekly basis, the volunteers
travel to local elementary and middle schools to teach children about science. The
lessons are fun, interactive, and designed in such a way as to stimulate their interest and
curiosity about science and the world around them. [1]
In order for children to fully grasp or become interested in a topic, they often
require interactive teaching with hands-on activities as well as visual aids. Models help
to stimulate curiosity and provide a deviation from routine textbook and lecture-style
learning. A common problem facing most teachers and the VSVS organization is a lack
of funding to purchase classroom models to aid in teaching. [2] The goal of this project
was to design an affordable model that is educational, hands-on, durable, easily
transported, and kid-friendly.
One of the topics that VSVS was particularly interested in teaching to the children
was the digestive system anatomy and physiology. Many physical models that are on the
market range in cost from five hundred dollars to well over one thousand dollars. [3] This
is not practical for a teaching budget. The models also do not show the flow
directionality through the digestive tract. The children can look at the models but most
do not involve any interaction.
A review of teaching websites and consultations with instructors suggested a
variety of possible ways for the model to portray the digestive system. The most
practical option was a physical model showing the relative sizes and locations of the
3
organs as well as the flow directionality. This would be educational, interesting to the
kids, and functional for VSVS to travel with frequently.
The project was divided into two tasks: the development of visual aids and the
building of the physical model. The visual aids would be designed at two different ageappropriate educational levels and the physical model would be flexible for use at all age
levels. The combination of a physical model, visual aids, demonstrations, and lesson
plans would allow VSVS to successfully teach a lesson about the digestive system to the
children as well as peak their interest about a new scientific topic.
4
METHODOLOGY
(A) Building of the Physical Model
This was the first focus of the project. Research through textbooks and websites
produced an outline of what would need to be included in the physical model. The
organs were drawn in detail and their actual relative sizes were noted. Many physiology
references contained a similar side facing head and upper torso. It was decided the
physical model would be of this shape as to show the full digestive system anatomy. An
appropriate material for the main human shape needed to be determined. After visiting
the hardware store and consulting with hardware professionals, a sheet of ¾ inch
plywood was selected as the support structure. This was still lightweight but thick
enough to support any attachments and not warp over time. Anything thinner would have
not been durable enough to withstand much force and anything thicker would have been
too heavy to be easily transported. This board was purchased and cut into shape (see
appendix A) being sure to smooth around the edges to prevent splinters and to provide a
more professional look to our model.
Next, it was important that the appropriate method was chosen to demonstrate to
the students the order of flow in the digestive system. One option to show the flow was
to use one long tube and attach it to the board in the direction of the organs. The main
problem with this idea was that one long tube would not allow for the demonstration of
the sphincter muscles and their role in stopping and allowing the flow of food.
Functioning valves would best portray the actions of the muscles. Joint valves with large
handles were selected to represent the muscles. Of all the tubing options, the plastic
tubing proved to be the most flexible (for bending and shaping onto the board) and the
5
most functional (clear in color to show the movement of fluids and food). Two different
sizes of tubing were purchased: ½ inch diameter as the esophagus and small intestine, and
¾ inch diameter as the large intestine. This tubing was joined together with plumbers
epoxy, liquid nails, superglue, and tightly wrapped electrical tape to prevent leaks around
joining ends. It was then laid out onto the main board (see appendix B) and attached
using plastic hooks and small ¼ inch screws.
After the tubing was attached, it was tested for leaks by squirting water into the
system. This was when the problem of air/water pressure was discovered. The tubing
was bent in such a way as to go against gravity forcing the need for a source of air large
enough to push the water throughout the entire system. Many options were experimented
with such as balloons, air pumps, squirt bottles, and human exhalation. A squirt bottle
roughly the size of a common ketchup bottle was chosen as the best option. The tip was
cut to fit directly over the end of the plastic tubing cutting off any air leaks. One forceful
squeeze of the bottle provided enough pressure to force the water throughout the tubing
system.
With the tubing system properly functioning, the organs were ready to be
attached. First, materials were experimented with to find the optimal characteristics
needed for the model. Plaster of Paris was purchased and shaped into organs. This
material was much too heavy for a model that needed to be transportable. Again, the
hardware professionals were consulted and the suggestion of lightweight spackle proved
to be the best option. The spackle was easy to shape, lightweight, durable, and dried
quickly. From previous research, the organs were formed into their correct shape and
relative size for the model. Liquid nails and epoxy were used to attach the organs to the
6
board. Parts of the tubing were left uncovered so that the students could watch the flow
through the organs.
Everything was allowed to dry thoroughly and sit for a week to ensure durability.
Latex paints were selected in appropriate colors and the organs were painted. A clear
glossy finish was spray painted over the entire model providing a slimy, realistic effect.
(see Appendix C)
Having completed most of the model, it was brought in for a presentation test-run.
This was when the need for a stand became evident. The stand needed to provide enough
support so the model could not easily be knocked over by children, yet it also needed to
fold up or come apart to aid in transportability. Two wooden legs ( ¾ inch plywood)
were nailed in place and a third hinged leg was nailed to the center of the back. A metal
chain attached helped the model to sit at the appropriate angle for demonstration. (see
Appendix D)
(B) Production of Visual Aids and Lesson Plans
It was necessary to have visual aids that coordinated with the physical model to
help the children get the most from the lesson. For the older children, a basic textbook
drawing was done with an additional poster containing the functions of each organ in the
drawing. (see appendix E ) A harder board was chosen instead of poster board giving
the visual aids more durability. For the younger children, the visual aids were made more
interactive with Velcro attached to the organs. The descriptions of the functions of the
organs were also attached to Velcro to allow the students to play a matching game
facilitating their learning. (see Appendix F)
7
An important concept for the kids to learn was the relative sizes of the intestines.
Since the physical model was not able to show this, 5 feet of 1 ½ inch tubing to represent
the large intestine. 21 feet of ½ inch plastic tubing was purchased to show the full length
of the small intestine.
Demonstrations are essential in keeping the attention of kids during a class period.
Flashcards were prepared for both age groups with questions appropriate for each age
level. Also for the younger kids, plastic bags were filled with labeled shapes of each
digestive organ. Enough were made for each child to have a bag so they could hold up
the organ in response to the flashcard question. The organs were cut out of construction
paper and laminated to ensure durability.
The lesson plans were designed after looking at previous lessons for the same age
groups. The younger children needed a lesson plan with less details and more
interruptions between teaching.
Lesson plans were created based upon the idea that the
VSVS team members would never be lecturing the classroom. Instead each lesson plan
is filled with various questions on various levels to keep the classroom interacting and
answering as the lesson progresses. (see Appendix G) Demonstration sheets were
provided with the lesson plans as a guide for the students to follow along with each organ
discussion. The demonstration sheets included a descriptive drawing of each organ,
listing an overview of the main functions of that organ, based upon the level of the
lesson. (see Appendix H)
In order to receive written feedback, both a student survey and a teacher survey
were passed out at the end of the lesson. The questions basically provided information as
to whether each person felt this lesson was productive and what could be done for
8
important. The student’s survey included reason for why or why not they enjoyed the
lesson. These surveys provided us with great information to include in our results section
and to revise our lesson plans. (see Appendix I)
9
RESULTS
It was important to see how students responded to our physical model, visual aids,
and lesson plan. We were able to visit an eighth grade classroom at Bass Middle School
in Nashville, TN. There we spent an hour working with students, teaching them about
“The Digestive System.”
The lesson was begun by asking the students if they had any previous knowledge
about digestion. Their lack of response showed the absence of prior physiological
education. This gave us a good starting point to test whether these students actually
benefited from our lesson.
10
The student’s response to the digestive story was one of humor and also showed
that the maturity was higher than the content of this story. Going back and forth between
the story, model, and visual aids reinforced the concepts of the digestive system to these
students. They were remembering the terminology and facts about each organ and its role
in the digestive system as a whole. It was abundantly clear how well they were grasping
the points we were trying to get across and how curious they were to learn more about the
digestive system with the many questions each student kept asking.
When we introduced the flash cards to the students, they all jumped at the chance
to hold up the paper organs as their answers. This was unexpected given the age of this
classroom. The excitement and enjoyment of each student became obvious when we ran
out of flash cards and they were wanting to answer more questions. The percentage of
students who were able to answer the questions accurately was impressive taking into
consideration they lack of knowledge about the digestive system they had as the lesson
started. The flash cards led to student volunteering to describe each organ’s function.
Students gathered around and watch the water flow through the physical model.
They were curious as to how these sphincters worked and wanted to see the model,
“George”, function repeatedly.
The teacher and student surveys were eagerly filled out and their responses were
overwhelming praises. The feedback was very helpful in determining that our model,
visual aids, and lesson plan was a success.
11
CONCLUSIONS
After multiple presentations and feedback from our advisor and other VSVS
faculty, the model has proved successful. Our actual classroom test and the feedback we
received was also evident of the achievement of our model. The model and lesson plan
seem to fit the needs of VSVS and are appropriate for the age groups intended. We have
given our project to our advisor and hope VSVS will get many years of use from our
model.
12
RECOMMENDATIONS
There is still analysis work remaining to be done on this project. Arrangements
have already been made with Mel Joesten and local teachers to visit their classes for
classroom testing of the model and lesson plan. Before the true success of the model can
be determined, it needs to be tested at a younger (3rd –5th grade) level. Feedback from the
students and teachers will lead to potential modification of the lesson plans so that they
will be more appropriate for teaching in the future.
VSVS can also test the model by sending it out with a group of students not
affiliated with its design. This would allow improvements in the teaching guides of the
model: how easy the lesson plan was to follow and timing of the lesson, etc. It would
also test the durability and functionality of the physical model itself.
These tests along with more feedback from use will lead to the completion of this
model and its integration into the VSVS collection of lessons. The goal is for this lesson
to become very popular among the school kids and one of the more fun and easy lessons
for the adults to teach. Also, success of this model may lead to similar reproductions for
other classrooms.
13
BIBLIOGRAPHY
[1]
“VSVS Online”. http://www.vanderbilt.edu/vsvs/overview.htm
[2]
Mel Joesten, Head of VSVS, Project advisor
[3]
http://www.einsteins-emporium.com/science/human-anatomy/sh430.htm
14
APPENDIX
(A)
15
APPENDIX
(B)
16
APPENDIX
(C)
17
APPENDIX
(D)
18
APPENDIX
(E)
19
APPENDIX
(F)
20
APPENDIX
(G)
THE DIGESTIVE SYSTEM LESSON PLAN
INTRODUCTION
*** read digestive story (approximately 5 minutes)
Ask Students: What is the purpose of the digestive system?
Answer: to break down food into units that can be absorbed and used by the body.
Points to include in discussion:
 Food gives fuel that allows us to move, think, and breathe.
 The amount of calories that a body uses each day varies depending on the
person’s size, weight, body build, occupation, and age.
Ask Students: Why does food need to be broken down?
Answer: Food is a fuel source for the body that cannot be used by the body until it is
broken down
Points to include in discussion:
 Basic components of food are proteins, sugars, fats, vitamins, minerals, and water.
 These components are further broken down into fundamental building blocks.
 Carbohydrates such as starch are broken down into simple sugars such as glucose.
 Fats are broken down into fatty acids and glycerol.
 Sugars and fats are used for energy
 Fats are used for insulation
 Proteins, vitamins, and minerals are used to build the structure of our body such
as the skeleton and skin.
21
DISCUSSION
THE MOUTH
Ask students: Where do you think the process of digestion begins?
Answer: in the mouth
Ask students: What does the mouth do to aid in digestion?
Answer:
Points to include in discussion:
 The purpose of the mouth is to initiate digestion
 Chewing causes the mechanical (physical) breakdown of food
 Saliva causes the chemical breakdown of food through a chemical substance or
enzyme called ptyalin
 Saliva is a liquid produced in the salivary glands found in the lining of the cheeks
 There are three pairs of salivary glands located in the front of the mouth below the
tip of the tongue, beneath the tongue, and in front of the ears.
 Saliva helps digestion by adding water and enzymes which serve to break down
some of the components of food.
 Saliva helps in swallowing by lubricating food and by holding it together
 Teeth assist in breaking down food by cutting, tearing, and grinding.
 A bolus is the ball of food and saliva that is shaped by the tongue during chewing
 A bolus is the end product of chewing
***demonstrate model (pour colored water into mouth)
THE ESOPHAGUS
Ask students: Where does food go when it leaves the mouth?
Answer: the esophagus
Points to include in discussion:
22




The esophagus is the 25 cm (10”) long muscular tube that connects the mouth
with the stomach
The esophagus is a separate tube from the windpipe (trachea), but the two do meet
in the lower pharynx
A small flap of tissue called the epiglottis automatically closes over your
windpipe when you swallow to keep food from entering the windpipe
It takes food about seven seconds to travel through the esophagus
Ask students: Can we swallow if we were upside down or in outer space?
Answer: yes
Points for discussion:
 Food travels down the esophagus because of peristalsis, a wavelike contraction of
muscles in the esophagus
 Peristalsis is so strong, that it can force good through parts of your digestive
system when you are lying down, standing on your head, or floating upside down
in the weightlessness of outer space
THE STOMACH
(CHEMICAL BREAKDOWN)
Ask students: Where does the food go when it leaves the esophagus?
Answer: the stomach
Points to include in discussion:
 The stomach continues the breakdown of food
 The stomach contains dilute hydrochloric acid and pepsin
 A thick mucus coat or lining protects the stomach from the harmful acids it
contains
 Pepsin is an enzyme in the stomach that breaks proteins into its building blocks—
amino acids.
 The stomach physically breaks down food with its strong muscular walls by
compressing and churning the food
 To keep the food in the stomach, sphincter valves are used to keep the stomach
closed
 The sphincter valves need to keep the acid-food mixture in the stomach so it
cannot escape back into the esophagus. The esophagus does not have the same
coating to protect it from the acids that are in the stomach
 Heartburn is caused by acid partially traveling up the esophagus
 Ulcers are caused when there is a hole in the stomach lining
 The stomach regenerates its lining every three days
23

When the food has been processed by the stomach it is called chyme.
***Remind students that the stomach also does mechanical and/or physical
breakdown of food as well.
THE SMALL INTESTINE
***Remind students that the food in the stomach is now called chyme
Ask students: Where does the chyme go when it leaves the stomach?
Answer: the small intestine
Points to include in discussion:
 When the food has been processed by the stomach into chyme, a sphincter
between the stomach and the small intestine opens. Peristalsis pushes the
food into the small intestine.
 The small intestine is 2.5cm thick and over 6m (18’) long.
 Food moves through the small intestine by peristalsis
 Most of digestion takes place in the small intestine
 The walls of the small intestine releases an intestinal juice that contains
several types of digestive enzymes that breaks the food into small units that
can be absorbed by the cells in the small intestine
 Food does not go through the liver and the pancreas, but these argans send
juices to the small intestine that assist in digestion
 After 3-5 hours, most of the food in the small intestine is digested
 The small intestine is the first area of absorption—the first place where
nutrients are absorbed from the food
 The small intestine has an inner lining that looks like wet velvet
 The inner lining of the small intestine is covered with millions of tiny
fingerlike structures called villi
 Digested food is absorbed through the villi into a network of blood vessels
that carry the nutrients to all parts of the body
 By the time the food is ready to leave the small intestine, it is basically free of
nutrients except water. What remains are undigested substances that include
water and cellulose (a part of fruits and vegetables).
***demonstrate length of intestines
LARGE INTESTINE
Ask students: Where does the chyme go when it leaves the small intestine?
Answer: the large intestine
24
Points to include in discussion:
 The large intestine is the final area of absorption in the digestive system
 The large intestine is shaped like a horseshoe that fits over the coils of the small
intestine
 The large intestine is about 6.5cm in diameter but only about 1.5 m long
 After spending about 18 – 24 hours in the large intestine, most of the water in the
undigested food is absorbed
 Materials not absorbed form a solid waste
***demonstrate model
REVIEW
Use flashcards and allow students to call out answers.
25
APPENDIX
(H)


THE DIGESTIVE SYSTEM
digestive system breaks down food into proteins, sugars, fats, vitamins, minerals, and water for
use by the body in the form of energy
digestive tract consists of mouth, esophagus, stomach, small intestine, and large intestine
MOUTH- -initiates digestion with physical breakdown of food, chewing
- -saliva from salivary glands initiates chemical breakdown of food
- -teeth break down food by cutting, tearing, and grinding
-at the end of chewing, tongue shapes food and saliva into a ball called a bolus
ESOPHAGUS-25 cm long muscular tube that connects the mouth to the stomach
-food takes 7 seconds to travel through esophagus in a muscular wave
like contraction motion called peristalsis
-no digestion or absorption takes place here
STOMACH-J-shaped organ that continues the breakdown of food with Hydrochloric acid and
pepsin
-strong muscular walls compress and churn the food
-regenerates its protective lining every 3 days
-once food is fully processed in the stomach, it is called chyme
SMALL INTESTINE-sphincter opens allowing chyme to enter small intestine from stomach
-2.5 inches thick and over 6 meters long and most of digestion takes place here
-intestinal juices break food into small units which can be absorbed by intestinal lining
(first place absorption takes place)
-after 3-5 hours most food is digested
-most all nutrients except water are fully absorbed here through finger-like structures
called villi that line the intestinal wall, nutrients are then carried through blood
vessels to all parts of the body
LARGE INTESTINE-final area of absorption
-shaped like a horseshoe and fits over the coils of the small intestine
-6.5cm thick and 1.5 meters long
-after 18-24 hours most of the water in undigested food is absorbed, rest of the material
is formed into a solid waste, feces, and exits anus
26
APPENDIX
(I)
27