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version 1.0 1 Rogue Community College Biology BI 102 – Introduction to Biology II
Lab #3: The Cardiovascular System
Name ______________________________
Prelab Questions (5 points)
Carefully read the entire lab, and answer the following Prelab Questions before your lab session.
- What are the names of the four chambers of the heart?
- Why are the walls of the left ventricle thicker than the walls of the right ventricle?
- What structures prevent the backwards flow of blood through the heart?
- The ______________ is a muscular wall between the left and right ventricles.
- Does the pulmonary artery carry oxygen rich or oxygen poor blood? _____/ 5
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Learning Objectives
Part A: Identify the following structures on the external portion of the mammalian heart: coronary arteries, apex, right auricle, left auricle, right ventricle, left ventricle, pulmonary vein, pulmonary artery, aorta, and vena cava. Part B: Identify the following structures within the mammalian heart and state the function of each: right atrium, left atrium, right ventricle, left ventricle, tricuspid (right atrioventricular) valve, mitral (left atrioventricular) valve, pulmonary semilunar valve, aortic semilunar valve, papillary muscles, chordae tendineae, vena cava, aorta, pulmonary artery, and pulmonary vein. Be able to trace the path of blood through the mammalian heart. Part C: Determine the heart rate and blood pressure by taking the pulse and using a blood pressure cuff. Explain the relationship between exercise, heart rate, and blood pressure.
version 1.0 4 The heart has valves between the chambers as well as between the ventricles and the vessels that exit the heart. Two valves separate the atria and ventricles. The tricuspid valve (right atrioventricular valve) separates the right atrium from the right ventricle, and the mitral valve (left atrioventricular valve) separates the left atrium from the left ventricle. These valves prevent the back flow of blood into the atria when the ventricles contract; a backward flow of blood will actually close the valves. When the ventricles contract, the papillary muscles in each ventricle also contract. The papillary muscles pull on the chordae tendineae and prevent the bicuspid and tricuspid valves from inverting. When the right and left ventricles contract, blood moves out of the ventricles and through the aortic and pulmonary semilunar valves, respectively. Each contraction of the heart pumps blood through the heart chambers and out into the arteries. The right ventricle pumps blood into the pulmonary trunk, which leads to the pulmonary arteries and eventually the lungs. The left ventricle pumps blood into the aorta, the largest artery in the body, which supplies blood to the rest of the body. The cardiac muscle of the heart has its own blood supply. The coronary arteries, which lie on the surface of the heart, branch off the aorta. The coronary veins drain the cardiac muscle’s blood supply into the right atrium of the heart. The coronary and other major arteries and veins of the heart are located in fat-covered grooves called sulci (singular, sulcus). The right atrium receives deoxygenated blood from the body and pumps the blood into the right ventricle. The right ventricle pumps blood to the lungs. Therefore, the right side of the heart is the pump for pulmonary circulation. The left atrium receives oxygenated blood from the lungs and sends the blood into the left ventricle. The left ventricle pumps the oxygenated blood out to the body tissues. The left side of the heart is the pump for systemic circulation. To make sure the upper and lower chambers of the heart do not work against each other during a heartbeat, the two atria contract simultaneously first, then the two ventricles contract at the same time. When the heart beats, the familiar lub-dub sound we hear is actually the noise made when the valves of the heart close. The first sound (lub) is low and dull, and lasts longer than the second sound. The lub is caused by the closing of the valves between the atria and ventricles, the left and right atrioventricular valves, following atrial contraction. After a brief pause, the second sound (dub) follows the first sound. The sound has a snapping quality of higher pitch and shorter duration. The dub sound is the closing of the aortic and pulmonary semilunar valves, the valves between the ventricles and the aortic and the pulmonary arteries. The contraction of the heart creates blood pressure. Systole is the term used when a heart
version 1.0 5 chamber is in contraction. Diastole is the term used when a heart chamber is in relaxation. The beat of the heart is controlled by special pacemaker cells in the heart tissue and the message is transmitted via special conducting cells in the heart tissue. Two special structures help control the movement of contraction messages: the SA (sinoatrial) node and the AV (atrioventricular) node. When the SA node initiates the heartbeat, the atria contract. When the AV node is stimulated, it causes the ventricles to contract. Blood pressure (BP) keeps blood moving in the blood vessels. Blood pressure is created by the contractions of the heart. Our pulse is caused by the expansion and recoil of the arterial walls during each heartbeat.
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- You will need to take a moment to observe the heart so it is positioned correctly for accurate identification (Figure 2.2). Note: Most heart diagrams show the left atrium and left ventricle on the right side of the diagram. Imagine the heart in the body of a person facing you. The left side of their heart is on that person’s left. Since you are facing them, it is on your right.
- Identify the right and left sides of the heart. Look closely and you will see a diagonal line of blood vessels that divide the heart on the anterior (front) side of the heart. This line contains the branches of the coronary arteries. The coronary arteries and their branches deliver oxygen and nutrients to the heart muscle itself. The half that includes all of the apex (pointed end) of the heart is the left side. Confirm this by squeezing each half of the heart. The left half will feel much firmer and more muscular than the right side. The left side of the heart has more muscle because it must pump blood to the entire body. The right side will feel softer and less muscular because it only pumps blood to the lungs.
- Turn the heart so that the right side is on your right, as if it were in your body. Examine the flaps of darker tissue on the top of the heart. These ear-like flaps are called auricles. Find the large opening at the top of the heart next to the right auricle. This is the opening to the superior vena cava, which brings blood from the top half of the body to the right atrium (the atria are the top chambers in the heart). Stick a probe down this vessel. You should feel it open into the right atrium.
- A little down and to the left of the superior vena cava there is another blood vessel opening. Insert your probe into this; it should also lead into the right atrium. This is the inferior vena cava, which brings blood from the lower tissues. You can also see another blood vessel next to the left auricle. This is a pulmonary vein that brings blood from the lungs into the left atrium.
- Sticking straight up from the center of the heart is the largest blood vessel you will see. This is the aorta, which takes oxygenated blood from the left ventricle to the rest of the body (the ventricles are the lower chambers of the heart). The aorta branches into more than one artery right after it leaves the heart, so it may have more than one opening on your heart specimen. Look carefully at the openings, you should be able to see they are connected to each other.
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- Behind and to the left of the aorta there is another large vessel. This is the pulmonary artery, which carries blood from the right ventricle to the lungs.
- Use dissection pins to mark the following: A. The pulmonary trunk or artery. B. The aorta. C. The right auricle D. The left auricle. E. The left ventricle. F. The right ventricle.
- In order to proceed to Part B of this lab, you must first show your instructor your properly labeled heart.
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- Set your sheep heart in the dissection tray, lift the ventral portion of the heart, and open it like a book. This is pictured in Figure 2.3.
- You will be using your probe to trace the path of blood through the heart starting at the superior vena cava. You will also be identifying structures within the heart along the way.
- Note where the inferior and superior vena cava enter the right atrium. When the atrium contracts, the blood is pumped from the right atrium to the right ventricle through the tricuspid (right atrioventricular) valve.
- Find the tricuspid valve which is located between the right atrium and the right ventricle. You may notice that it looks like three membranous flaps.
- The membranes of the tricuspid valve are connected by tendons to papillary muscles on the walls of the ventricles. These tendons are called the chordae tendineae or "heartstrings." The tricuspid valve allows blood to enter the ventricle from the atrium, but it prevents backflow from the ventricle into the atrium.
- Identify the right ventricle. When the ventricle contracts, the blood is pumped out of the heart through the pulmonary semilunar valve and into the pulmonary artery. The pulmonary semilunar valve functions to prevent blood from flowing back into the right ventricle. The pulmonary artery takes blood to the lungs where it is oxygenated.
- Oxygen rich blood flows back to the heart through the pulmonary vein and into the left atrium.
- When the atrium contracts, the blood is pumped from the left atrium to the left ventricle through the mitral (left atrioventricular) valve.
- Find the mitral valve which has two membranous flaps connected to papillary muscles by chordae tendineae. This valve is also known as the bicuspid valve; it allows blood to enter the ventricle from the atrium, and it prevents backflow from the ventricle into the atrium.
- Note the thick walls of the left ventricle (compare to the walls of the right ventricle) that are needed to pump blood through the systemic circuit. When the left ventricle contracts, blood is forced out of the heart through the aortic semilunar valve and into the aorta. The aorta delivers blood to the body.
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- Use dissection pins to mark the following: A. The left ventricle B. The right ventricle C. The tricuspid valve D. The mitral valve E. The papillary muscles in the left ventricle F. The chordae tendineae in the left ventricle G. The right atrium H. The left atrium
- Show your instructor your properly labeled heart.
- Use your probe to trace the path of blood through the heart from the vena cava to the lungs and from the lungs to the aorta, and fill in the following blanks. You may find it helpful to observe the anatomical charts and models of the heart while completing this activity.
- Venae Cavae 7. Lungs
- ________________________ 8. ________________________
- ________________________ (valve) 9. ________________________
- ________________________ 10. ________________________ (valve)
- ________________________ (valve) 11. ________________________
- ________________________ 12. ________________________ (valve)
- Lungs 13. Aorta
- Place your sheep heart back in the plastic bag from which it came, and dispose of it in a biohazard bag. Wash your dissecting tools with soap and water, dry them, and return them to their proper receptacles.
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- Pulmonary circulation carries blood between the heart and the lungs. Systemic circulation carries blood to the rest of the body. a. In what chambers of the heart does pulmonary circulation begin and end? b. In what chambers does systemic circulation begin and end?
- Compare the thickness of the wall of the superior and inferior vena cava and the aorta. Which is thicker and why?
- Under what conditions in everyday life would you expect the heartbeat (and the blood pressure) to increase? When might this be an advantage? A disadvantage?
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- List the function of the following structures: a. Papillary muscles b. Chordae tendineae c. Atrioventricular valves (A/V valves) d. Semilunar valves
- Articulate a question that pertains to today’s lab but was not answered by doing today’s lab. _____/ 5
