Materials Included In Kit

Additional Materials Required

Safety Precautions

Food dye will stain skin and clothing. Wear chemical splash goggles, chemical-resistant gloves 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 model heart may be emptied by untaping one end of one of the balloons to drain the liquid. Rinse the tubing with distilled or deionized water and allow it to dry completely before storing for later use.

Lab Hints

• Enough materials are provided in this kit for 24 students working in groups of four or for six groups of students. This laboratory activity can reasonably be completed in one 90-minute class period. If the activity is divided into two 45-minute classes, Part A may be completed the first class and Parts B and C in the second class. The prelaboratory assignment may be completed before coming to lab, and the worksheet questions may be completed the day after the lab.
• Heart models may be reconstructed for different classes. Simply cut and remove the electrical tape and balloons. Replacement balloons are available in the Flinn Scientific Catalog/Reference Manual, Catalog No. AP1900.

Answers to Prelab Questions

1. What portion of the heart do the balloons represent in this laboratory experiment?

   The balloons represent the four chambers of the heart—the right atrium, right ventricle, left atrium and left ventricle.

2. Why is it crucial that the clamps do not allow any blood flow when they are not specifically opened?

   The clamps represent valves of the heart. Valves cannot allow backflow of blood to previous chambers of the heart therefore it is important that the clamps do not allow backflow as well.

Answers to Questions

1. Draw a picture of the model heart labeling what each component represents.
   {10997_Answers_Figure_5}
2. Compare and contrast the heart model and an actual mammalian heart. How are they similar? How are they different?

   The model heart is similar to a mammalian heart in that it has four chambers, valves between chambers and direction of flow. It is different in that it does not function autonomously (it requires assistance to pump and open/close valves). It also simplifies the model by not showing the blood as it travels throughout the lungs and other organs. It simply displays the path the blood takes in relation to other areas of the heart.

3. The heart pumps blood through the lungs and the rest of the body. Although the heart model does not biologically represent the lungs and other organs, is it physiologically correct in displaying the pumping action of the heart?

   Physiologically, the heart is a closed system that pumps blood to and from itself. The lungs and the rest of the body are a series of tubes connecting one pump to another. If the blood in the simulated heart model moves in the same pattern/path found in a human circulatory system it is correct without displaying all the anatomical relationships with other organs.

4. Plaque can form on arteries due to unhealthy diet as well as other factors. How could the heart model be modified to simulate the effects of plaque buildup in the arteries?

   Plaque-filled arteries could be simulated by using tubing with a smaller diameter. Plaque buildup forms inside the arteries which decreases the area in which blood is able to travel.

5. The heart forms before any other organ in the mammalian body. Based on the simplicity of this model why does it make sense that the heart develops before other organs?

   The heart begins by pumping blood to itself in the initial stage of embryonic growth. As the rest of the body develops, the path which the blood travels through before returning to the heart becomes more complex but still follows the same pattern.

6. Why do both atria contract simultaneously? Hint: Use an additional reference source as necessary.

   The SA (sinoatrial) node is the heart’s natural pacemaker. Cardiac muscles are coupled impulses from the SA node that spread rapidly through the walls of the atria causing both atria to contract in unison.

References

Brock, D. Working Model Hearts. The Science Teacher. 2009, 76, pp 36–40.

Campbell, N. A. Biology, 6th Edition; Benjamin Cummings: San Francisco, 2002; pp 875–877.

Introduction

The heart acts as the “pump” of the cardiovascular system. Pressure created in the heart drives blood throughout the entire circulatory system. Build a model to see how the heart pumps blood!

Concepts

• Cardiology
• Atria vs. ventricles
• Blood flow

Background

A heartbeat makes a sound similar to “lub-dub.” Although the sound of a heartbeat seems simple, each heartbeat is actually a very precise series of events.

Each side of the heart has a valve which assists in moving blood from the atrium to the ventricle. The tricuspid valve controls blood flow from the right atrium to the right ventricle. The mitral valve controls blood flow from the left atrium to the left ventricle. These two valves are responsible for the “lub” portion of the “lub-dub” sound (see Figure 1).

The period of time from the beginning of one heartbeat to the next is known as the cardiac cycle. Each cycle (heartbeat) has two phases—the diastole and the systole. The diastole is the time when the heart muscle relaxes. The systole is the time when the heart muscle is contracting. During diastole, the atria and ventricles of the heart relax and start to fill with blood. After the atria are filled with blood, the atria contract causing the tricuspid and mitral valves to open and the blood to flow into the ventricles. This series of events is known as atrial systole. After atrial systole, the atria begin to relax again and the valves close so the atria can refill with blood. The ventricles contract and pump the blood out of the heart.

Heart valves ensure that blood flows in only one direction. Valves that function properly open and close in sync with the pumping of the atria and ventricles. Each valve has flaps that open and close. The mitral and tricuspid valves must be closed when the ventricles contract so that blood can exit the heart to other parts of the body without backflow into the atria. Valves also exist between the ventricles and the rest of the body. When the right ventricle contracts it pumps blood out to the pulmonary artery through the pulmonary valve. On the left side of the heart the mitral valve allows blood to flow from the left atrium to the left ventricle without backflow. Once the left ventricle fills with blood it contracts. This process is known as ventricular systole. As blood exits the left ventricle to the aorta it passes though the aortic valve. The aorta is the main artery that carries blood away from the heart to the rest of the body. The aortic valve closes quickly to prevent backflow into the left ventricle.

Experiment Overview

Build a functioning heart model using balloons, rubber tubing and adjustable plastic clamps. Apply pressure to the chambers and manipulate clamps to understand how the heart pumps blood to the rest of the body.

Materials

Prelab Questions

1. What portion of the heart do the balloons represent in this laboratory experiment?
2. Why is it crucial that the clamps do not allow any blood flow unless they are specifically opened?

Safety Precautions

Red food dye will stain skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Part A. Building the Model

1. Using scissors cut the plastic tubing into four pieces of the following lengths—two 6" pieces, one 12" piece and one 18" piece.
2. Obtain four balloons—each balloon represents a chamber of the heart. Using a black permanent marker label the four balloons as follows: RA (right atrium) RV (right ventricle) LA (left atrium) LV (left ventricle)
3. Obtain the RA balloon and cut a tiny hole in the rounded end of the balloon (see Figure 2). Tip: The hole should be just big enough so that when it is stretched it will fit snuggly over one end of the tube.
4. Insert one end of one of the 6" tubing pieces into the hole cut into the RA balloon.
5. Secure the end of the RA balloon around the tube using a rubber band (see Figure 2).
   {10997_Procedure_Figure_2}
6. Cut a 5" piece of electrical tape. Stretch the tape and wrap it tightly over the portion of the tubing already covered with the balloon and rubber band (see Figure 3). Tip: It is best to only tape over portions of the balloon that have tubing underneath. Taping over folds in the balloon will increase the likelihood of leaks.
   {10997_Procedure_Figure_3}
7. Insert the free end of the 6" tubing into an adjustable plastic clamp. Continue to pull the tubing through until the clamp is located in approximately 3" from the end of the tubing.
8. Obtain the RV balloon and repeat steps 6 and 7 using the free (opposite) end of the 6" tube attached to the RA balloon.
9. Using the technique described above continue to assemble the heart model according to the diagram in Figure 4. Note: Steps 3 and 4 are only necessary when attaching the round end of the balloon.
   {10997_Procedure_Figure_4}
10. Although the lungs and body are not built into the model, label the tubing to indicate when the blood flows to those locations (see Figure 4).

Part B. Adding Simulated Blood

11. Using a graduated cylinder, measure 100 mL of distilled or deionized water.
12. Add one drop of red food coloring to the cylinder of water and stir. The red water represents the blood.
13. Ensure that all adjustable plastic clamps are in the open position.
14. One member of the group should hold the LV balloon at approximately shoulder level.
15. With a second group member holding the free end of the 18" piece of tubing, gently begin to pour the 100 mL of simulated blood into the tube. Pour slowly so that no “blood” is spilled.
16. Carefully stretch the open end of the LV balloon to fit over the free end of the 18" tube.
17. Using a 5" piece of electrical tape secure the LV balloon to the 18" tube as done in step 6.
18. Check the model for minor leakages and secure with additional electrical tape if necessary.

Part C. Heart Model Operation

19. Open all the clamps and manipulate the heart model so that half of the blood is in the right atrium (RA) and the other half is in the left atrium (LA).
20. Once the blood has flowed to the proper chambers close the clamps so that the blood remains in the designated chambers.
21. To demonstrate how the heart pumps blood from one chamber to another, one student should operate the clamps (valves) and another should hold the right atrium (RA) in one hand and the left atrium (LA) in the other hand.
22. As soon as the atria are squeezed the tricuspid valve and the mitral valve should be opened so that blood can flow from the right atrium to the right ventricle and from the left atrium to the left ventricle.
23. Once the blood has passed into the appropriate chambers close both valves.
24. One student should hold the right ventricle (RV) in one hand and the left ventricle (LV) in the other hand.
25. As the ventricles are squeezed another group member must open the pulmonary valve and the aortic valve.
26. Once the blood has flowed from the right ventricle to the left atrium and from the left ventricle to the right atrium the valves must be closed again.

Student Worksheet PDF

10997_Student1.pdf