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PPT Cardiac Cycle Developer Notes Version 01 02 Date 2003/06/25 Who SC DK What Initial version Would be nice to have simple, clear diagram of the heart. I don’t know how to make one or where to get one. DK - It would be nice to have a good visible working model of a pump with a valve, especially one that pumped in a circuit. Demo a pump with no valves first, like a syringe. Blowing up a balloon (nice, simple, cheap, the valve is your fingers, but there is no circuit like blood vessels) peristaltic pump (not really valved), pitcher pump (valve is hard to see), bicycle pump (valve is hard to see), ball pump (valve is hard to see. My little bulb-type pump is more heart-like), bailing pump (valve is hard to see), chemical barrel pump (valve is hard to see), squirt gun (might be the best, could we run a tube from the output back to the reservoir?), modified syringe (how to valve? A ball didn't work as a valve), I’m trying to keep the physiology terms general and simple, should I be more specific? Or, is it too complex already?? Not sure how “appropriate” an activity w/ stethoscopes would be? Are our stethoscopes good enough? Will other schools have them? Goals Have the students understand how the heart works as a pump. Have the students understand what occurs during the cardiac cycle (heartbeat). Concepts & Skills Introduced Area Physiology Physiology Physics Concept Cardiac cycle Heart, arteries, veins Pumps Time Required Warm-up Questions How does blood move around? How does the heart act like a pump? Presentation It seems weird to present the cardiac cycle starting with late diastole, but it’s easier to explain starting with the heart at rest. Diseases of the cardiovascular system are the leading cause of death in the United States. This would be a good topic for a research project. 840992106 sc PPT Cardiac Cycle Any diagrams or models of the heart that you may have (or borrow from the biology department) would greatly aid the discussion. Assessment Writing Prompts Relevance Answers to Exercises Answers to Challenge/extension 840992106 sc PPT Cardiac Cycle Activity 1. Use a stethoscope to listen to your heart. What do you hear? 2. Harvey’s vein experiment: Hang one arm at your side for a few seconds, then place the arm, palm facing up, on a table. Notice the blue veins of the inner arm. With your other hand, press your index finger against one of the veins. With slight pressure, run your thumb along the vein toward your heart. What happens? Release your index finger. What happens? Repeat, except press with your thumb and run your index finger along the vein away from the heart. What happens? Summary 1. The heart sounds are often described as “lub-dup.” “Lub” occurs during systole and “dup” occurs during early diastole. What events do you think you are actually hearing? 2. What conclusion do you think William Harvey made about direction of blood flow in veins? What conclusion do you think he made about valves in veins? 840992106 sc PPT 840992106 sc Cardiac Cycle PPT Cardiac Cycle Background/History In the early 1600’s an English physician, William Harvey, discovered the circulation of blood in the human body. He was a contemporary of Galileo and actually attended the university where Galileo was a teacher. Much as physics did, physiology at the time relied on ideas from the ancient Greeks. Much like Galileo, William Harvey insisted on experimentation. With careful observations and experimentation, Harvey disproved earlier theories about the heart and blood and became a father of modern physiology! William Harvey studied what we call the circulatory or cardiovascular system. Cardio refers to heart, and vascular refers to blood vessels. The heart acts as a pump. This means that the heart relies on differences in pressures to move the fluid (blood) around. The heart is a muscle with four internal chambers. The two upper chambers are called atria. The atria collect blood. Blood vessels called veins feed into the atria. The two lower chambers are called ventricles. Blood passes from the atria into the ventricles. The ventricles squeeze blood out of the heart and into blood vessels called arteries. The main arteries from the ventricles then branch off, taking the blood where it needs to go (body or lungs)! The right side of the heart collects blood from the body and pumps it to the lungs. The left side collects blood from the lungs and pumps it to the body. Valves in the heart control the flow of blood in the heart. Valves between the atria and ventricles are called atrioventricular (AV) valves. They prevent blood from going back up into the atria when the ventricles are contracting. Valves between the ventricles and arteries are called semilunar valves (because the look kind of like half-moons). They prevent blood from going back into the ventricles. The process of getting blood into the heart and then pumping it out is called the cardiac cycle. One complete cycle is what we know as a heartbeat. Let’s look at the stages of the cardiac cycle: Late diastole: The heart is relaxed during this phase and the pressure inside the heart is low. Blood from veins (where the pressure is relatively higher) drains into the atria. At the end of this phase the atria squeeze blood into the ventricles. Systole: The ventricles contract and the pressure within them increases (remember Pascal’s principle!). Blood is pushed into the arteries (where the pressure is relatively lower). The AV valves are pushed shut to prevent blood from going back up into the atria. Early diastole: The heart begins to relax, the semilunar valves close preventing blood from going back into the ventricles. The pressure inside the heart begins to drop and the cycle continues! The main arteries from the heart eventually divide into a network of smaller arteries. The smaller arteries eventually become thin-walled capillaries where nutrient and waste exchange occurs. The capillaries turn into a network of veins that eventually feed into the main veins that feed into the atria. Since the pressure in veins is low and since much of the blood in veins has to flow against the force of gravity, veins rely on skeletal muscle contractions to push blood back to the heart. Veins also have valves that keep blood flowing in the right direction! 840992106 sc PPT Cardiac Cycle Exercises 1. Upon seeing a man stabbed with a dagger, William Harvey observed that blood was rhythmically spurting out of him. What type of blood vessel was damaged? Explain. 2. Do fluids flow from high pressure to low pressure, or low pressure to high? 3. Congestive heart failure occurs when the heart pumps inefficiently due to weakness of or damage to the heart muscle. Explain how this causes blood to “back up” in the heart chambers and lungs. 4. With careful observation of the hearts of dying animals (and even newly hanged humans), Harvey noticed that the atria contract before the ventricles. In what stage of the cardiac cycle does this occur? 5. The cardiac cycle normally lasts about 0.8 seconds. How many heartbeats normally occur per minute? What might be some factors that alter the length of the cardiac cycle? Challenge 1. Explain what happens when your hand or foot “falls asleep” (the “pins & needles” feeling). 840992106 sc