Lab 4: THE CARDIOVASCULAR SYSTEM 1

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1 Lab 4: THE CARDIOVASCULAR SYSTEM 1 LABORATORY OBJECTIVES At the end of this laboratory, you should be able to: 1. Identify parts of the heart and learn the path of blood through the heart. 2. Through dissection, identify the parts of the heart and follow path of blood. 3. Learn how to measure blood pressure and what that represents. INTRODUCTION ROOT WORDS That may help your understanding: cardio=heart vascular=blood vessels peri= around endo=inner epi=outer inter=between myo=middle atrium=entry hall ventricle=little belly auris=ear septum=partition superior=above inferior=below sinus= hollow The cardiovascular system is responsible for transporting nutrients and oxygen to all of the body s tissues, and for carrying waste and carbon dioxide away. At the centre of this system is the heart. The heart is the workhorse of the cardiovascular system, pumping an estimated five litres of blood every minute when the body is at rest. Of course, this rate increases during times of activity or stress. The vascular system has an approximate network length of 100,000 kilometres of blood vessels, and the heart must pump with enough pressure to supply all of these with oxygen rich blood. The relative size of the heart is small in comparison to the scope of work it must do over a lifetime. The hollow, cone shaped organ is the approximate size of your fist, and sits in the relative centre of your chest. The apex, or point, of the heart is slightly tilted to the left, and the bottom left quadrant is larger and stronger, which is likely why its beat is more readily heard on the left side of your chest. The heart is surrounded by a triple layered, bag like membrane called the pericardium. This fibrous, inflexible membrane serves to protect and anchor the heart. The pericardium is made of connective tissue fused to the diaphragm, and keeps the heart in place. The sack that is created by the pericardium contains a viscous fluid (pericardial fluid) that acts as lubricant to reduce friction between the membrane and the heart as the heart moves during contractions. The outer wall of the heart itself is made of three layers; the epicardium or outer layer, the myocardium, or middle layer, and the endocardium, or inner layer. Both the epicardium and 1 The Introduction, Activity 1, 2 and 4 are from Bio 103 Lab 9:The Cardiovascular System.pdf and accessible via Creative Commons license at: 1

2 endocardium act as lining layers to create a smooth surface and reduce friction on the middle layer. The myocardium is made of cardiac muscle fibres and is the bulk of the heart and responsible for its pumping action. The heart is effectively divided into four parts, or chambers, each with its own muscle mass separated by a thin layer of connective tissue. The superior chambers are named the left and right atria (atrium singular), and are separated by connective tissue called the septum. Each of the atria has an attached appendage called an auricle (named so, as it looks like a dog s ear) that increases its volume. The two inferior chambers of the heart are called the left and right ventricles, and are likewise separated by the septum. The thickness of the walls in each of the chambers varies according to their functions. The atria have much thinner walls than the ventricles, as they only pump blood into another chamber of the heart, whereas the ventricles have a much heavier workload pumping blood destined for the lungs and the rest of the body. This is explained in further detail below. Blood is pumped through the heart into two circulatory systems; the pulmonary system (the lungs) and the systemic system (the rest of the body). In the pulmonary system, deoxygenated (oxygen poor) blood enters the right atrium from the various parts of the body via three major vessels: the superior vena cava (from the upper body), the inferior vena cava (from the lower body), and the coronary sinus (from the wall of the heart). From the right atrium, blood flows to the right ventricle and is pumped to the lungs via the right and left pulmonary arteries (one goes to each lung). At the lungs, deoxygenated blood releases carbon dioxide and takes on oxygen, becoming oxygenated (oxygen rich). The blood then returns to the heart via the four pulmonary veins and is emptied into the left atrium, where it now goes into the systemic circulatory system. The left atrium pumps the blood into the left ventricle, where it is then pumped into the ascending aorta. The aorta and its branches carry the oxygenated blood to the various body tissues and the heart muscle itself. Because the blood needs to travel such a great distance throughout the body, the left ventricle is the most robust of the four chambers and can have two to four times the muscle mass of the right ventricle( that pumps blood to just the lungs). To prevent backflow of blood into the heart chambers, each is equipped with a valve that can control the flow. Valves are made of thick connective tissue surrounded by endocardium, and they open and close in response to pressure changes in the heart as it contracts and relaxes. There are two types of valves: atrioventricular and semilunar. The valves found between the atria and ventricles are called atrioventricular valves and consist of flaps that respond to pressure changes in the ventricle. When the ventricles are relaxed between pumps, the valve flaps open (pointing into the ventricle) and blood can move from the atrium into the 2

3 ventricle. When the ventricle is contracting and full of blood, the valve flaps are forced shut and stop the blood from backwashing into the atrium. These valves are slightly different in the right and left sides of the heart. Between the right atrium and ventricle the valve has three flaps and is thus referred to as a tricuspid valve, and between the left atrium and ventricle the valve has two flaps and is referred to as a bicuspid or mitral valve. Semilunar valves are found on both the pulmonary artery and the aorta, and function to keep blood from flowing backward into the ventricles of the heart. The semilunar valves get their name from the three half moon shaped cusps they have that allow the blood to flow in only one direction. The pumping action of the heart is regulated by rhythmical electrical activity that activates the cardiac muscle. There are a small fraction of cardiac muscle fibres that become self excitable (or autorhythmic) during embryonic development. During the rest of your life, these cardiac fibres play an essential role in acting as a natural pacemaker for your heart as well as coordinating the contractions of the heart so they work as an effective pump. If you have ever been double bounced on a trampoline, you have experienced coordinated pumping; if the timing is off, both trampoline jumpers lose momentum. This can be much like the response of uncoordinated heart chambers. Fortunately, because the heart is regulated by electrical impulses, we are able to easily record its action using an electrocardiogram to amplify its electrical activity. The size and timing of the waves recorded during a cardiac cycle can give us insight into irregular heart rhythms. The pumping action of the heart produces waves of blood that surge into arteries leading away from the heart. These pressure waves results in the body s pulse. There are number of arteries that have sufficient blood volume and are close enough to the surface of the skin to allow us to measure our pulse by touch. The diagram to the right identifies these locations and their associated arteries. 3

4 ACTIVITY 1: IDENTIFYING HEART FEATURES to be done BEFORE the lab MATERIALS Coloured pencils Heart diagram (provided) METHODS 1. Photocopy, trace, or draw a heart diagram such as the one on the following page then label your own diagram with the same numbered parts as shown on the following page. 2. On your own heart diagram, using arrows show the path of blood as it moves through the heart. 3. Colour the pathways of deoxygenated blood blue, and oxygenated blood pathways red. 4. Include your labeled and colored diagram in your data/observations section of your lab report. DISCUSSION QUESTIONS 1. Write a flow chart listing the direction of blood flow through the heart. 2. Which ventricle is more muscular and why? (2 marks) 4

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6 ACTIVITY 2: HEART DISSECTION 2 In this activity you and your partner will be dissecting a heart to help you learn the parts and the direction of blood flow through the heart by better understanding the anatomy of the heart. There are no discussion questions for this activity. MATERIALS Whole mammalian heart (cow, sheep, or pig) the heart should not have been deveined or cleaned Scalpel or dissection scissors Forceps Dissecting tray Probe Gloves 5% bleach solution METHODS SHEEP, COW OR PIG HEART DISSECTION Sheep, cows, and pigs have a four chambered heart, just like humans. By studying the anatomy of their hearts, you can learn about how your own heart pumps blood through your body. You will be using a heart obtained from the butcher or local grocery store. Because the heart you will be dissecting will be considered food grade, you will need to treat it in the manner you would for any raw meat. The heart will be stored at 4 C (the temperature of your fridge) until you are ready to dissect it. Use your dissecting tray and tools while examining the heart. You will be wearing gloves, but remember to wash them before you touch anything else or remove them and get a fresh pair. To decontaminate the equipment and area after use, spray with a 5% bleach solution and rinse 3 times with water. An antibacterial kitchen spray will also be sufficient. The heart can be disposed of in the garbage, though it is recommended that you wrap seal it in a plastic bag to reduce odors. 2 Adapted from by Bio 103 Lab 9:The Cardiovascular System.pdf: which was adapted from Biology Corner ( 6

7 OBSERVATION: EXTERNAL ANATOMY Most heart diagrams show the left atrium and 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 their left, but since you are facing them, it is on your right. 1. Your heart may still be covered by the pericardium. It is a thin membrane surrounding the heart. You will need to remove this membrane before commencing with the rest of the dissection. Carefully cut an incision with your scalpel into the membrane from top to apex. Be cautious not to damage the underlying cardiac tissue. The pericardium should easily peel away from the heart. 2. Identify the right and left sides of the heart. Look closely and on one side you 11 Page will see a diagonal line of blood vessels that divide the heart. The half that includes the entire 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 is stronger because it has to pump blood to the whole body. The right side only pumps blood to the lungs.) 3. 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 3. 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 3 Auricle = an earlike appendage on both the right and left atria that increases the volume of each atria 7

8 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. 4. 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 (remember 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 and you should be able to see that they are connected to each other. 5. Behind and to the left of the aorta there is another large vessel. This is the pulmonary artery which takes blood from the right ventricle to the lungs. DISSECTION: INTERNAL ANATOMY 1. Insert your dissecting scissors or scalpel into the superior vena cava and make an incision down through the wall of the right atrium and ventricle, as shown by the dotted line on the right in the external heart picture. Pull the two sides apart and look for three flaps of connective tissue. These tissues form the tricuspid valve between the right atrium and the right ventricle. The flaps are connected to the papillary muscles on the ventricle walls by tendons called the chordae tendinae or "heartstrings." This valve allows blood to enter the ventricle from the atrium, but prevents backflow from the ventricle into the atrium. 2. Insert your probe into the pulmonary artery and see it come through to the right ventricle. Make an incision down through this artery and look inside it for three small membranous pockets. These form the pulmonary semilunar valve which prevents blood from flowing back into the right ventricle. 3. Insert your dissecting scissors or scalpel into the left auricle at the base of the aorta and make an incision down through the wall of the left atrium and ventricle, as shown by the dotted line on the left in the external heart picture. Locate the mitral valve (or 8

9 bicuspid valve) between the left atrium and ventricle. This will have two flaps of membrane connected to papillary muscles by tendons. 4. Insert a probe into the aorta and observe where it connects to the left ventricle. Make an incision up through the aorta and examine the inside carefully for three small membranous pockets. These form the aortic semilunar valve which prevents blood from flowing back into the left ventricle. 5. Take the time at the end of your dissection to show and describe to your partner the direction of blood flow through the heart. 9

10 ACTIVITY 3 4 : Measuring Blood Pressure Blood pressure is measured in millimeters of mercury (mm Hg). A typical blood pressure is 120/80 mm Hg, or "120 over 80." The first number represents the pressure when the heart contracts and is called the systolic blood pressure. The second number represents the pressure when the heart relaxes and is called the diastolic blood pressure. In this activity you will practice taking your blood pressure. MATERIALS Stethoscope Sphygmomanometer (blood pressure cuff) METHODS 1. Deflate the air bladder of the cuff and place it around the upper arm so it fits snugly, but not too tight. If you re right handed, you should hold the bulb/pump in your left hand to inflate the cuff. Hold it in the palm so your fingers can easily reach the valve at the top to open and close the outlet to the air bladder. 2. Put the head of the stethoscope just under the edge of the cuff, a little above the crease of the person s elbow. Hold it there firmly with the thumb or with the fingers of the right hand. Listen. 3. Inflate the cuff with brisk squeezes of the bulb. Watch the pressure gauge as you do it, you should go to around 150 mmhg or until the pulse is no longer heard. At this point blood flow in the underlying blood vessel is cut off by pressure in the cuff. 4. At around 150, slightly open the valve on the air pump (held in your left hand). This part takes practice, it s important that you don t let the air out too suddenly or too slowly. 5. Now, pay attention to what you hear through the stethoscope as the needle on the pressure gauge falls. You will be listening for a slight blrrp or something that sounds like a prrpshh. The first time you hear this sound; note the reading on the gauge and immediately following you should hear the sound of a pulse. This value is the systolic blood pressure. 6. The sounds should continue and become louder in intensity. Note the reading when you hear the sound for the last time at the point you stop hearing the pulse. This is the diastolic blood pressure. 4 From: Biology Corner: 10

11 7. Afterwards, open the air valve completely to release any remaining pressure. You and your partner should perform this operation twice. Record your blood pressure and your partners: Blood pressure Partner 1 Blood pressure Partner 2 Systolic blood pressure Diastolic blood pressure Blood Pressure DISCUSSION QUESTIONS 1. Blood pressure is highest just after ventricular systole, and lowest during ventricular diastole, explain? (3 marks) 11

12 References: Jenkins, D. a. (1996, 07 10). Retrieved 02 1, 2010, from Electrocardiogram Library: Musopf. (n.d.). Cardiovascular System. Retrieved 01 10, 2010, from Biology Corner: Tortora, G. a. (1993). Principles of Anatomy and Physiology. New York: Harper Collins College Publishers. Vodopich, D. a. (1992). Biology Laboratory Manual, third Edition. St Loius: Mosby Year Book. This lab was compiled from parts of many other labs thanks to those who were kind enough to share their work: Bio 103 Lab 9:The Cardiovascular System.pdf: Biology Corner: The components of blood and their importance - video 12