Physiological Modeling of the Digestive System



Physiological Modeling of the Digestive System



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.

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 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 age-appropriate 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.

METHODOLOGY

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 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 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)

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 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)

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.

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.

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.

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.

BIBLIOGRAPHY

[1] “VSVS Online”.

[2] Mel Joesten, Head of VSVS, Project advisor

[3]

APPENDIX

(A)

APPENDIX

(B)

APPENDIX

(C)

[pic]

APPENDIX

(D)

APPENDIX

(E)

[pic]

APPENDIX

(F)

[pic]

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.

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:

• 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

• 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

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.

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

APPENDIX

(I)

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