Materials Included In Kit

Additional Materials Required

Prelab Preparation

Prepare the following solution for Part A. Stomach Digestion.

• To prepare pepsin, add 600 mL of tap water to a 1000-mL beaker. Add 12.0 g of pepsin and gently stir to dissolve in the water. (Adjust quantity based on class size. Use 2.0 g of pepsin per 100 mL of water). For Part A, each group needs 40 mL of pepsin.
• Distribute 40 mL of the HCl solution to each group or have a central location for students to obtain the HCl.

Prepare the following solution for Part B. Enteric-Coated Pill Challenge.

• To prepare pepsin for one trial, add 300 mL of tap water into a 500-mL beaker. Add 6.0 g of pepsin and gently stir to dissolve in the water. (Adjust quantity based on the class size. Use 2.0 g of pepsin per 100 mL of water). For Part B, each group needs 20 mL of pepsin per trial. Enough pepsin is included for two trials.
• For each trial, distribute 20 mL of the HCl solution to each group or have a central location for students to obtain the HCl.

Safety Precautions

Hydrochloric acid is slightly toxic by inhalation and ingestion, a severe body tissue irritant and corrosive to the eyes. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant gloves when working with an acid, heat-resistant gloves when handling hot glassware and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The pepsin and hydrochloric acid mixture may neutralized with base and then rinsed down the drain with plenty of excess water according to Flinn Suggested Disposal Method #24b. The excess pepsin may be handled according to by Flinn Suggested Disposal Method #26b. Any excess hydrochloric acid may be neutralized with base and then rinsed down the drain with plenty of excess water according to Flinn Suggested Disposal Method #24b.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students.
• The prelaboratory assignment may be completed before coming to lab and the analysis may be completed the day after the lab. Part A can be completed in one 50-minute class period. Only 35–40 minutes of data will be collected. This is enough time to show how the food dissolves or degrades in the stomach juices. Part B can be completed in one 50-minute class period for one trial. Two 50-minute class periods will be needed for two trials.
• To allow students maximum time to complete the activity, have the water baths ready and warmed to 40 °C prior to beginning class.
• The pH of stomach acid is 2. The combination of HCl and pepsin should yield a pH near 2.

Teacher Tips

• This activity can be utilized during a body systems unit including the implementation of a STEM activity. Students design their own pill coating that must sustain 20 minutes within an acidic environment.
• It is ideal that each group have its own simulated stomach acid and water bath for Part A. During Part B, two groups may share one stomach acid and water bath beaker.
• The four recipes in sample data table 2 successfully covered two pony beads entirely.
• The enzyme pepsin acts on protein within the stomach. Amylase, an enzyme in the saliva and the small intestine, acts on carbohydrates and pancreatic lipase aids in the breakdown of lipids.
• When testing enteric coatings, recipes with corn starch dissolved with the shortest time. Recipes with flour lasted well over an hour. Water and olive oil seemed to have similar effects on the coating. Sugar decreased dissolving time, but not excessively.
• Extensions can include requirements to the amount of enteric coating surrounding the pill. This can be achieved by having a weight restriction. The pony bead can be covered using about 1 gram of enteric-coating. Another challenge is to have the medication be taken with food, which would require a longer lasting enteric coating, perhaps lasting 2 or more hours. Another extension could be requiring the students to design an enteric coating that dissolves in a certain length of time, perhaps between 45–50 minutes simulating a needed effectiveness such as a diabetic taking oral medication prior to eating. A final extension is to challenge the students to design an enteric coating that endures the stomach (acidic environment) and dissolves in the small intestine (basic environment) where the medication would be absorbed.

Answers to Prelab Questions

1. What acid is present in stomach juices?
   

   Hydrochloric acid is the acid found in gastric juices.

2. Describe the safety hazards and precautions to be taken when working with strong acids.
   

   When working with strong acids, like HCl, you should limit inhalation as it is an irritant. Avoiding contact with eyes and skin is very important and wearing goggles, gloves and an apron will reduce the risk of contact.

3. List the advantages of using an enteric-coated pill over a non-coated pill.
   

   Pills are coated with an enteric coating for one of two main reasons. First, the enteric coating will prevent the medication from dissolving in the stomach, which often causes irritation and discomfort. Secondly, enteric coatings protect the medication from being partially degraded in the acidic environment of the stomach.

Sample Data

Data Table 1. Stomach Digestion of Food

Data Table 2. Enteric Coating Recipe

Multiple recipes were tested a minimum of two trials. Results for four pills are included. See Teacher Tips for additional information.

Answers to Questions

1. During Part A, what observations were made about the different food items tested?
   

   Accept all reasonable answers. The Lifesaver completely dissolved/broke down within 15 minutes. The stomach acid solution turned the color of the Lifesaver and smelled sweet. The black olive discolored to a light brown. The color moved from the outside toward the center and there was slight swelling. The corn tortilla remained intact showing very little change. The flour tortilla slowly lost its shape and became mushy, however very little seemed to have dissolved.

2. Of the possible ingredients used in Data Table 2, predict the order the ingredients will dissolve, fastest to slowest, based on data collected from Part A.
   

   Accept all reasonable answers. Most likely, students will observe the sugary food dissolved the fastest. They may invert the flour substance and oil substance, however, the corn tortilla should be the slowest to dissolve as it seemed unaffected by the stomach acids.

3. How did the information from Part A assist in the design of the enteric coating for your pill?
   

   Based on the sample observations, one might expect a pill coating with oil and corn starch to withstand the acidic environment of the stomach, given the corn tortilla was relatively unaffected by the stomach acids and the black olive only lost coloration. A pill covered with flour or sugar substances would most likely dissolve in the stomach acid.

4. Explain the recipe you used for the enteric coating for your pill. Describe what ingredients were used, why each was chosen and how the product performed as a pill coating.
   

   Student answers will vary.

5. What changes did you make to the recipe to improve upon your enteric coating recipe? Why?
   

   If students used corn starch they most likely did not have an enteric coating that lasted 20 minutes. They may switch to different ingredients like flour or sugar or a combination for the next trial.

6. What other variables could impact the longevity of the enteric coating on the pill? Explain your reasoning.
   

   Answers may include temperature (water bath and stomach acids are supposed to be maintained at 40 °C), whether the pill is taken with or without food, the pH of the stomach acids (stomach acid is typically a pH of 2, a higher or lower value may affect the enteric coating).

7. If you were asked to design an enteric coating for a medication to be taken with food, how would you alter your recipe?
   

   If medication is taken with food, then the time for it to enter the small intestine for absorption would lengthen. This would mean that a pill coating would need to last longer than 20 minutes. For this lengthened time, an increase in the amount of flour in the enteric coating recipe and a decrease in the corn starch or sugar ingredients may be needed.

8. Pepsin is an enzyme that actively breaks down protein within the stomach. If you were required to use protein in the enteric coating of your pill, explain how this would change the effectiveness of your pill coating.
   

   If protein was a requirement for the enteric coating pill design, it would start to dissolve the coating while in the stomach juices. Increasing the amount of flour with the protein ingredient might help reduce the dissolving time. Also the pill would need to be taken on an empty stomach to allow the medication to enter the small intestine as quickly as possible.

References

Beaumont, W. Experiments and Observations on the Gastric Juice and the Physiology of Digestion. Pittsburgh, Allen, 1833.

Introduction

Many people get upset stomachs when taking medication like aspirin. Why does this occur and what can be done to prevent this? In this two-part lab, you will investigate the digestion process and then design a pill coating to prevent discomfort when taking medication.

Concepts

• Digestion
• Food processing
• Engineering design
• Human physiology

Background

Food processing takes large pieces of food and breaks them down into smaller molecules the body can use. Organic materials consisting of protein, fats and carbohydrates cannot be used directly by cells because they are too large to pass through a cell membrane. Also, the molecules ingested are not identical to those found and needed in the body’s cells. In order to break down the food into absorbable molecules, mechanical fragmentation and chemical digestion must occur.

Digestion, in humans and all mammals, begins in the mouth with chewing. Saliva protects the mouth lining, lubricates food to ease swallowing, prevents tooth decay by buffering acids from food and enzymes and kills bacteria that enters with food. Food moves from the mouth to the stomach by peristalsis, contractions of smooth muscles that push the food down the esophagus. Once food enters the stomach, it will be stored and then digested. The stomach secretes digestive fluids, called gastric juices, which mix with the food as the stomach wall churns. The gastric juices are very acidic and have a high concentration of hydrochloric acid. The pH is around 2 and has the ability to dissolve iron nails! The acid degrades the extracellular matrix that binds cells together, kills bacteria and hydrolyzes protein using the enzyme pepsin. How does our stomach avoid being destroyed by this highly acidic environment? First, pepsin is secreted in an inactive form called pepsinogen. Pepsinogen does not become active until mixed with hydrochloric acid. Hydrochloric acid and pepsin are released by different cells, which prevents mixing until entrance into the lumen (cavity) of the stomach. Secondly, a protective coating of mucus is released by the stomach’s epithelial cells. These epithelial cells are damaged by the acidic environment, however. As a result, they go through mitosis rapidly and the entire stomach lining is replaced every three days. Food continues to be broken down, and as the stomach churns it creates a nutrient-rich broth called chyme. This thick fluid is passed into the small intestine in small amounts for 2–6 hours until the stomach is emptied. Digestion is completed in the small intestine. Bile and pancreatic enzymes mix with the chyme to complete the breakdown of carbohydrates, proteins and lipids.

An interesting historical look into digestion was conducted in the 1800s by an Army doctor, William Beaumont (1785–1853). Dr. Beaumont treated a patient with a musket shot to the abdomen. The soldier, Alex St. Martin, recovered from his wound but healed with a 10-centimeter wide fistula (tunnel) that led from his stomach to the outside of his body. St. Martin had to cover the hole to prevent food and liquids from oozing out. Dr. Beaumont seized the opportunity to experiment on Alex St. Martin by hiring St. Martin to work for him. Dr. Beaumont conducted experiments on St. Martin related to digestion within the stomach. He would place pieces of food tied to a string into the stomach through the tunnel and remove them later to see what digestion had occurred. Here are some excerpts from Dr. Beaumont’s records.

August 1, 1825. At 12 o’clock, a.m., I introduced through the perforation, into the stomach, the following articles of diets, suspended by a silk string, and fastened at proper distances, so as to pass in without pain: a piece of high seasoned a la mode beef; a piece of raw, salted, fat pork; a piece of raw, salted lean beef; a piece of boiled, salted beef; a piece of stale bread, and a bunch of raw, sliced cabbage; each piece weighing about two drachms; the lad continuing his usual employment around the house.

At 1 o’clock, p.m., withdrew and examined them—found the cabbage and bread about half digested: the piece of meat unchanged. Returned them to the stomach.

At 2 o’clock, p.m., withdrew them again—found the cabbage, bread, pork, and boiled beef all cleanly digested, and gone from the string; the other pieces of meat but very little affected. Returned to the stomach again.

At 3 o’clock, p.m., examined again—found the a la mode beef partly digested: the raw beef was slightly macerated on the surface, but its general texture was firm and entire. The smell and taste of the fluids of the stomach were slightly rancid; and the boy complained of some pain and uneasiness at the breast. Returned them again.

So, what exactly happens to food once it enters the stomach? Do certain foods digest more quickly than others? What causes pain and uneasiness as digestions occurs? The last question is one that chemists, engineers and pharmacists continue to study in order to develop pill coatings that do not dissolve until after they have passed though the stomach. When pills break down in the stomach, two issues may arise. The medication may be released into the stomach causing irritation, which occurs with aspirin. Or without a protective coating, the medication may be partially degraded in the acidic environment of the stomach, which occurs with the antibiotic erythromycin. Specially coated pills, called enteric-coated pills, have been designed to prevent either of these two issues by protecting the medication until it has passed through the stomach. Varying the material or thickness of the pill coating can change the effects of the medication on the body. Engineers play important roles from developing and testing chemical coatings to designing machinery that mass produces uniformly coated pills.

Experiment Overview

The purpose of this experiment is two-fold. First, the breakdown of food will be observed in a simulated stomach. Based on the data collected, a pill coating will be designed that is capable of surviving the acidic environment of the stomach. The enteric-coated pill should not dissolve in the stomach as this often leads to discomfort or medication degradation.

Materials

Prelab Questions

1. What acid is present in stomach juices?
2. Describe the safety hazards and precautions to be taken when working with strong acids.
3. List the advantages of using an enteric-coated pill over a non-coated pill.

Safety Precautions

Hydrochloric acid is slightly toxic by inhalation and ingestion, a severe body tissue irritant and corrosive to the eyes. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant gloves when working with an acid, heat-resistant gloves when handling hot glassware and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Follow all laboratory safety guidelines.

Procedure

Part A. Stomach Digestion

1. Prepare a water bath by adding 800 mL of water to a 1,000-mL beaker.
2. Place the beaker onto a hot plate at a low setting and allow the water to heat up to 40 °C. Note: Be sure to use heat-resistant gloves when handling hot lab equipment.
3. While the water is warming, prepare the simulated stomach by placing a 6" x 6" plastic bag into a 250-mL beaker. Secure the bag with the rubber band (see Figure 2).

4. Carefully place the 250-mL beaker into the water bath to make sure it fits safely and does not cause water to overflow.
5. Remove the 250-mL beaker from the water bath.
6. Prepare the simulated stomach juices by measuring 40 mL of pepsin with the 50-mL graduated cylinder. Pour the 40 mL of pepsin into the plastic bag.
7. Measure 40 mL of 0.2 M hydrochloric acid with the 50-mL graduated cylinder. Slowly pour the 40 mL of HCl into the plastic bag.
8. Place the 250-mL beaker with the stomach juices into the water bath with a thermometer. Raise the temperature to 40 °C then maintain at that temperature. The beaker may need to be removed from the hot plate intermittently to maintain the proper temperature.
9. While waiting for stomach juices to reach the proper temperature, prepare all four food items by attaching a long string securely to each item (see Figure 3).

10. Once the temperature reaches 40 °C, place each of the four food items into the stomach juices. The food items must be completely submerged while the string hangs over the beaker allowing for removal and observation.
11. Record the changing conditions of the food items, the temperature and the stomach juices every five minutes, for 40 minutes in Data Table 1 of the Digestion Connection Worksheet.
12. Remove the 250-mL beaker from the water bath and gently swirl the stomach juices every 10 minutes to simulate the churning of the stomach wall. Note: the pH of the stomach juices is very acidic, wear gloves while swirling. If any acid is spilled, notify the instructor immediately.
13. Consult your instructor for appropriate disposal procedures.

Part B. Enteric-Coated Pill Challenge

In this part of the lab, the challenge is to design an enteric-coated pill that will not dissolve within the acidic environment of the stomach. When medication is taken, the doctor will indicate whether or not to take the medication with food. In an empty stomach, it typically takes a pill 5–15 minutes to pass through the stomach into the duodenum, the first part of the small intestine. With a full stomach, it can take up to 3 hours for the medication to enter the duodenum. The challenge is to design an enteric-coated pill that remains in the acidic environment of the stomach for 20 minutes to ensure breakdown does not occur until inside the duodenum.

1. Create a recipe for an enteric coating to cover a pony bead, which represents the pill. The enteric coating should not dissolve in the stomach juices. Use data from Part A to help design the enteric coating.
2. As you create the enteric coating, record the recipe in Data Table 2 on the worksheet.
3. Using a weighing dish and a balance, measure the exact amount of solid ingredients used.
4. Using s separate 10-mL graduated cylinder, measure the exact volume of liquid ingredients used.
5. Combine the ingredients in the paper cup using the spatula.
6. Once the desired consistency is achieved, tie a long string to the pony bead.
7. Coat the entire pony bead with the enteric coating. No color of the pony bead should be visible.
8. Allow the enteric coating to dry while the water bath and simulated stomach are prepared.

1. Fill a 250-mL beaker with 150 mL of water. Place the beaker onto a hot plate at a low setting and allow the water to heat to 40 °C.
2. Place a 4" x 6" plastic bag into a 100-mL beaker and secure with a rubber band. Check that the 100-mL beaker fits securely into the 250-mL beaker water bath without causing water to overflow. Remove 100-mL beaker.
3. Measure 20 mL of pepsin with the 50-mL graduated cylinder. Pour into the plastic bag of the 100-mL beaker.
4. Measure 20 mL of 0.2 M HCl with the 50-mL graduated cylinder and slowly pour the HCl into the plastic bag with the pepsin.
5. Place the 100-mL beaker with stomach juices into the water bath with a thermometer and allow it to warm to 40 °C.

9. Using pH paper, measure the pH of the stomach juices. Record pH in Data Table 3.
10. Once 40 °C is maintained, add the enteric-coated pony bead to the stomach juices. Maintain the temperature near 40 °C. This may require removing the beaker from the hot plate intermittently.
11. Record the temperature and observations every five minutes for 20 minutes in Data Table 3.
12. Gently swirl the 100-mL beaker with stomach juices every 10 minutes to simulate the churning of the stomach wall. Note: the pH of the stomach juices is very acidic, wear gloves while swirling. If any acid is spilled, notify the instructor immediately.
13. Review your results, effectiveness of your enteric-coated pill and alter your recipe to improve your results. Record your second enteric-coated pill recipe and test results in Data Tables 4 and 5.
14. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

11293_Student1.pdf