KEY CONCEPTS AND PROCESS SKILLS. 3. Blood is pumped around the human body by the heart.

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1 Heart Parts to 1 50-minute session ACTIVITY OVERVIEW L A B O R ATO R Y SUMMARY Students investigate the functions of the blood vessels and the major structures of the heart. This activity offers an excellent opportunity for students to compare models and diagrams to real structures. After developing an understanding of the structures and function of the circulatory system, students can explore the structure of an actual heart in an optional dissection. KEY CONCEPTS AND PROCESS SKILLS 1. Human body systems are composed of organs. The structure of an organ is adapted to perform specific functions within one or more systems. 2. Each system within the human body is defined by the functions that it performs. For example, the heart, blood, arteries, veins, and capillaries are a part of the circulatory system, whose function is to transport gases (oxygen and carbon dioxide), nutrients, and wastes within the body. 3. Blood is pumped around the human body by the heart. 4. Valves control the direction of flow and allow liquid to move under pressure in both a pressure bulb and in the human heart. 5. The human heart is a double pump, which increases the efficiency of blood circulation. 6. The human heart is divided into four chambers (right ventricle, right atrium, left ventricle, left atrium). One side of the heart pumps blood directly to the lungs, while the other side of the heart pumps blood to the rest of the body. 7. The greater the surface area available for contact, the faster oxygen and carbon dioxide can diffuse from blood vessels into and out of the body s tissues. The capillary network provides surface area for this diffusion to take place. Teacher s Guide B-143

2 Activity 23 Heart Parts KEY VOCABULARY arteries atrium (plural: atria) blood vessels capillaries circulatory system function structure valves veins ventricle MATERIALS AND ADVANCE PREPARATION For the teacher 1 Transparency 23.1, Circulation in Mammals and Fish 1 transparency of Student Sheet 23.1, Heart Diagram * 1 overhead projector For the class * 2 3 stethoscopes (optional) * alcohol swabs For each student 1 Student Sheet 23.1, Heart Diagram * red and blue colored pencils For the Extension For the teacher * 1 video camera hooked up to a TV monitor (optional) For the class OR For each pair of students * 1 sheep heart * soap * paper towels * disinfectant spray * sponges * supply of water * 1 quart-size plastic bag with airtight seal * 1 pair of large dissection scissors * 1 thick paper plate (or a foam meat-packing tray) For each student * 1 pair of non-latex gloves 1 Student Sheet 23.2, Heart Dissection *Not supplied in kit B-144 Science and Life Issues

3 Heart Parts Activity 23 MATERIALS AND ADVANCE PREPARATION (CONT.) To find sheep hearts, look in your phone directory under Meat Wholesale or Meat Packers. You can also use other mammalian hearts, such as deer hearts. One heart per two students is ideal, but one heart per four students also works. If you are pressed for time and funds, do the dissection as an interactive, whole-class demonstration. This works best if you have a video camera that can hook up to a TV monitor. If not, consider splitting the class in half, with another activity for half of the class while you perform the dissection with the other half. TEACHING SUMMARY Getting Started 1. Introduce the relationship between the heart s structure and its function in providing continuous blood flow. Doing the Activity 2. Students use Student Sheet 23.1, Heart Diagram, to investigate concepts presented in a reading. Follow-Up 3. The class reviews key concepts and discusses the Analysis Questions. Extension Students perform or the teacher demonstrates the dissection of a heart. Teacher s Guide B-145

4 Activity 23 Heart Parts BACKGROUND INFORMATION Circulatory System In the human heart, blood enters through the atria. The right atrium receives blood from the body and the left atrium receives blood from the lungs. Although they appear smaller than the ventricles, the atria contain the same volume of blood during a heartbeat as the ventricles. The walls of the atria are thinner and more elastic than the walls of the ventricles, so they have a greater capacity to expand as they fill with blood. (If you do the dissection, students will be able to feel this difference in chamberwall thickness for themselves.) Ventricles pump blood to all parts of the body. Ventricle walls are thicker than the walls of the atria because they exert a much greater force than do the walls of the atria. The right ventricle pumps blood to the lungs for oxygenation, while the left ventricle pumps blood to the rest of the body. The body tissues contain far more capillaries for blood to move through than the lungs do. This means that the blood leaving the left ventricle needs to be pumped harder in order to get it through the extensive capillary beds of the body s tissues. For this reason, the wall of the left ventricle is thicker and stronger than the wall of the right ventricle. This double-pump system (present in mammals and birds) is more efficient than a single-pump system, such as in fish. In mammals, the blood pressure is boosted after the blood gets back from the lung capillaries, allowing it to be pumped much faster around the body. This is essential to supply the high oxygen and nutrition requirements of the cells of homeotherms such as birds and mammals. The heart valves work in opposition. When the right atrium is filled with blood, the valve between the atrium and ventricle is closed. As it opens to allow blood to flow into the ventricle, the valve between the ventricle and pulmonary artery closes. Occasionally a valve is not formed correctly at birth or deteriorates due to medications or disease and does not close completely. This can be heard through a stethoscope and is known as a heart murmur. Heart murmurs can also be caused by other defects, such as a hole in the septum (wall) between the ventricles. Arteries always carry blood away from the heart. All arteries in the body except the pulmonary arteries carry oxygenated blood. Since the pulmonary arteries are carrying blood away from the heart to the lungs, they are carrying deoxygenated blood. In pictures, arteries are always red. In reality, arterial blood is bright red. Veins always carry blood to the heart. All veins in the body except the pulmonary veins carry deoxygenated blood. Since the pulmonary veins are carrying blood to the heart from the lungs, they are carrying oxygenated blood. In pictures, veins are always shown as blue and vessels seen through the skin do appear blue. In reality, venous blood is dark red. REFERENCES Smith, Anthony. The Body. George, Allen and Unwin, B-146 Science and Life Issues

5 Heart Parts Activity 23 TEACHING SUGGESTIONS GETTING STARTED 1. Introduce the relationship between the heart s structure and its function in providing continuous blood flow. Teacher s Note: You can greatly enhance this reading by using heart models, showing video clips of the heart pumping blood, and/or doing the dissection extension. Ask, How does the heart maintain a one-way flow of blood through your body? Students are likely to mention the pressure bulb and valves investigated in the previous activities. Ask, Do you think heart valves will be similar to or different from the valves in the pressure bulb? Explain that they will be looking more closely at the structure of the heart and thinking about how the structure helps the heart to perform its pumping function. DOING THE ACTIVITY 2. Students use Student Sheet 23.1, Heart Diagram, to investigate concepts presented in a reading. Provide each student with a copy of Student Sheet 23.1, Heart Diagram. Have students read the activity, stopping periodically to complete the Stopping to Think sections by using their student sheets. Use Transparency 23.1, Circulation in Mammals vs. Fish, to review the double-pumped double loop of the circulatory system in mammals and birds. Contrast this with the single loop of the circulatory system in fish, which requires only a single pump. If you have stethoscopes, let students take turns trying to hear the lub-dub sound (described in the reading) of their own hearts. Wipe the earpieces with an alcohol swab between students. Tell them that they will investigate heart sounds in more detail by listening to an audio tape in Activity 26, Heart Sounds. FOLLOW-UP 3. The class reviews key concepts and discusses the Analysis Questions. Make a transparency of Student Sheet 23.1 to display while you review students ideas about how the heart works. Review the four-chambered double-pump structure of the heart. The left side of the heart functions as one pump to circulate oxygenated blood to the organs. The right side of the heart functions as a second pump to circulate deoxygenated blood to the lungs for oxygenation. The presence of two separate pumps for these separate functions increases the efficiency of the heart. The structure and location of the valves help to maintain the continuous, one-way flow of blood through the system. Large arteries and veins allow the blood to enter and leave the heart, while small capillaries allow for close proximity between the blood and tissues of the organs. Refer students to Student Sheet 23.1, which they colored in oxygenated and deoxygenated blood. Discuss the Stopping to Think questions, especially 3b and 3c. The pulmonary arteries, unlike other arteries in the human body, carry deoxygenated blood. The right atrium receives deoxygenated blood from the body. The blood then enters the Teacher s Guide B-147

6 Activity 23 Heart Parts right ventricle, from which it is pumped to the lungs via the pulmonary arteries. (The mnemonic Arteries come from the heart-ery may help students identify the function of arteries.) The pulmonary veins, unlike other veins in the human body, carry oxygenated blood. The left atrium receives oxygenated blood from the lungs. The blood then enters the left ventricle, from which it is pumped to the body via the aorta. As you discuss Analysis Question 2, some students may point out that nothing prevents the valves from flapping backward into the atria. You could then show students how attachments prevent this from happening, as shown in Figure 2 of Activity 26, Heart Sounds, on page B-73 in the Student Book. Heart valves can be damaged from rheumatic heart disease or from calcification due to old age. Damaged valves allow some blood to leak backward and, although the damaged heart continues to work hard, the output of blood is reduced. This results in a decreased oxygen supply to the tissues. People with serious heart valve disease are likely to feel chronically tired and are often unable to physically exert themselves. Inform students that they will be listening to the effects of valve failure in Activity 26, Heart Sounds. Decide whether students are ready to be assessed on the function of the heart. You can score student responses to Question 3 using the Applying Relevant Content element of the UNDERSTANDING CON- CEPTS (UC) variable. Extension Students perform or the teacher demonstrates the dissection of a heart. Depending on your school, community, and personal policies with regard to dissection, you may wish to perform a dissection of a sheep heart. Students often react strongly to dissections. Some consider it the most memorable and interesting thing they have ever done in science. Others find it unpleasant or feel that it is unethical. Dissecting organs from animals already used to provide meat is more likely to be acceptable to individuals who object to sacrificing animals solely for dissection. Be prepared to have an alternative assignment for students who do not want to participate. Some students may be more comfortable wearing latex gloves as they perform the dissection. (Make sure they are not allergic to latex. If a student shows an allergic reaction to latex, get medical attention immediately.) In all dissections or activities involving animals, model respect for life. Dissections demonstrate structure and function relationships and allow students to see how models relate to the real object. Heart dissections are fairly straightforward, although it is best to practice ahead of time if you have never done one (see Student Sheet 23.2). Safety Note: Before students start, discuss how to use the scissors safely. Students should take turns cutting. Warn students against trying to work together, with one holding the heart while the other cuts. This can easily result in cut fingers. Distribute Student Sheet 23.2, Heart Dissection. Students can use as this as a guide to record their notes during a class demonstration or to guide their own dissections. It is designed to minimize the time you have to spend demonstrating what to do and to maximize their time exploring this organ. Distribute the hearts. Have students feel the thickness of different parts of the heart and think about the functional reasons for any differences they feel. B-148 Science and Life Issues

7 Heart Parts Activity 23 At the end of the class period, students should put the dissected heart into a large, seal-able plastic bag. They should wash and dry the scissors, wipe the desk tops with disinfectant, and wash their hands with soap after the dissection. To review the dissection extension, discuss Analysis Question 1 on Student Sheet 23.2 ( What did the dissection teach you that would have been hard to learn in other ways? ) with the class. At this point, you may also wish students to discuss the trade-offs involved in classroom dissections. Student responses may include that they would not have realized the toughness of the valves, vessels, and cords in the heart if they had not dissected one. They could also feel for themselves the elasticity and strength of the heart muscle. In addition, the dissection may also have helped them understand the three-dimensional structure of the heart. Students should begin to develop an understanding of how real structures are represented in diagrams and models. Many characteristics of actual structures cannot be fully represented and, in many cases, have been simplified. Some students may also have enjoyed practicing surgical skills during the dissection. SUGGESTED ANSWERS TO ANALYSIS QUESTIONS 1. How is the structure of the heart related to its function? The function of the heart is to pump blood around the body. In order to perform this function, it has to be able to move the blood efficiently in one direction. If the heart were like a siphon bulb, it would not be able to maintain the one-way flow of blood. In order for the heart to pump blood around the body in one direction only, it has to have valves. Students may also note the greater thickness of the ventricular walls, especially the left ventricle, which pumps blood to the body. 2. What structures prevent blood in the ventricles from backing up into the atria? Why is it important for your heart to have these structures? The valves prevent backup of the blood from the ventricles to the atria. When the ventricles contract, the valves close and prevent blood from flowing back into the atria. The valves are important for the heart to be able to pump blood in one direction only. 3. Explain what is meant by the statement: The heart is two pumps. You may want to draw a diagram to support your explanation. A level 3 response follows. A level 4 response may include a reference to the difference between the double circulation of mammals and the single circulation of fish, as presented on Transparency UC The heart pumps blood to the body. The arc blood goes through the body and comes back to the heart. The heart then pumps this blood to the lungs. The blood comes back to the heart before it goes through the body again. One pump pumps blood to the body, and the other pump pumps blood to the lungs. This is why the heart is really two pumps. Teacher s Guide B-149

8 Circulation in Mammals and Fish Mammal Circulation blood to body capillaries in lungs blood from lungs heart capillaries in body Fish Circulation capillaries in gills 2006 The Regents of the University of California heart capillaries in body Science and Life Issues Transparency 23.1 B-151

9 Name Date Heart Diagram Arteries to head and arms Vein from head Aorta Pulmonary artery Pulmonary artery Pulmonary veins Left atrium Right atrium Left ventricle Right ventricle Vein from body 2006 The Regents of the University of California Science and Life Issues Student Sheet 23.1 B-153

10 Name Date Heart Dissection Safety: Use caution when cutting with the scissors. Hold the heart carefully. Do not try to have one partner hold the heart while another cuts. This can result in cut fingers. 1. Before you cut, examine the outside of the heart as described below. a. Find the main area of muscle at the base of the heart. These are the ventricles. Record how they feel. b. Find the small arteries that supply the muscles of the ventricles with blood. Draw a few of the arteries on the diagram below The Regents of the University of California c. Find the floppy-looking sacks at the top of the ventricles. Use your diagrams from the Reading in Activity 23 to help you decide what these sacks are. Record your ideas below. 2. Put a finger through one of the large tubes coming out of the top of the heart and feel around inside one of these sacks. Record your observations in the space below. Think about how the structure of these tubes helps them do their job. Science and Life Issues Student Sheet 23.2a B-155

11 Name Date Heart Dissection (cont.) 3. Now cut the heart as shown in the diagram. 4. Decide which of the vessels (large tubes) at the top of the heart carry blood into the heart. Hint: Look for the flap-like valves that will let your finger move more easily in one direction than the other. Label these vessels as veins on the diagram shown in Step Identify an atrium and a ventricle. Identify and describe the structures that prevent blood from flowing back into the atrium when the ventricle squeezes. 6. Look again at the atrium and ventricle. Find where the blood leaves the heart. Put your finger through this opening. Label these vessels (large tubes) as arteries on the diagram shown in Step If you have time, dissect the other half of the heart. a. Compare the thickness of the ventricles. b. Explain which side of the heart will pump blood more forcefully. c. Based on their functions in pumping blood to the body and to the lungs, explain any differences you observe between the left and right ventricles The Regents of the University of California ANALYSIS 1. Reflection: What did the dissection teach you that would have been hard to learn in other ways? Science and Life Issues Student Sheet 23.2b B-157