Download Developer Notes - University of Hawaii

PPT
Cardiac Cycle
Developer Notes
Version
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02
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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.
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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
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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?
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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!
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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).
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