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PPT
Cardiac Cycle
Developer Notes
Would be nice to have simple, clear diagram of the heart. I don’t know how to make one
or where to get one.
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?
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.
Any diagrams or models of the heart that you may have (or borrow from the biology
department) would greatly aid the discussion.
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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
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Cardiac Cycle
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 have valves that keep blood flowing
in the right direction!
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?
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?
6.
Challenge
1. Explain what happens when your hand or foot “falls asleep” (the “pins & needles”
feeling).
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