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Module 2
Exchange and transport
1.2.7 The cardiac cycle
Learning Objectives
• Understand the cardiac
cycle
Success Criteria
• Explain the terms cardiac cycle,
diastole, atrial systole and
ventricular systole
(Grade E - D)
• Explain how the valves work in
the cardiac cycle
(Grade C –B)
• Describe the cardiac cycle with
reference to the action of the
valves in the heart
(Grade B – A)
Starter
• Gently press a fingertip on your neck just one
side of your windpipe
• Each time the heart beats, you should feel the
pulse caused by a surge of blood through one
of your arteries that goes to your head
• If relaxed should feel a pulse roughly every
second
• The time between each pulse is the length of
the cardiac cycle.
Heart valves
• AV valve links the atria to
ventricles
• SL valves link ventricles to
pulmonary artery and aorta
• Why are valves important?
• Stop blood flowing the wrong
way
• Valves open and close
depending on the relative
pressure of the heart
chambers. High pressure
behind a valve forces it open.
•Explain how the valves work in the cardiac
• Circulatory system_1.wmv cycle (Grade C –B)
The cardiac cycle
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1. Atrial Systole
• Heart is full of blood
• Contraction of both atria,
decreasing volume of
chamber and increasing
pressure inside chamber
• AV valves open, SL
valves close
• blood flows  ventricles
• No backflow as veins
have valves
2. Ventricular Systole
• Atria relax
• Ventricles contract (0.1s
after atria)
• Decrease in volume =
Increase in pressure in
ventricle
– Forces AV valves to close
to prevent backflow
– Semi-lunar valves open
– blood flows from
ventricles  arteries
• Lasts ~0.3 s
3. Ventricular Diastole
• Ventricles and atria both relax
• High pressure in pulmonary artery &
aorta closes SL valves to prevent
backflow into ventricles.
• Blood returns to heart & atria fills
again due to high pressure in vena
cava and pulmonary vein.
• Increase in pressure of atria, as
ventricles continue to relax , their
pressure falls below that of the atria
and so AV valves open
• Blood flows passively into ventricles
from atria.
• Atria contracts – whole process
restarts
The cardiac cycle
Tasks
1) Describe each
stage of the
cardiac cycle,
referring to the
action of the
valves in each
stage.
•Explain the terms cardiac cycle, diastole,
atrial systole and ventricular systole
(Grade E - D)
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A
B
C
Changes in pressure in the heart during one heart beat
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Questions
•Describe the cardiac cycle with reference
to the action of the valves in the heart
(Grade B – A)
•
•
•
•
•
•
1. When does the blood start flowing in the aorta?
2. Are the semi-lunar valves open or closed at point B?
3.Why is ventricular volume decreasing at point C?
4. Calculate the heart rate
ANSWERS
1. Point A ventricles are contracting (AV valves are shut)
forcing blood into the aorta
• 2. Closed, ventricles are relaxed and refilling, so
pressure is higher in the pulmonary artery and aorta
forcing SL valves close
• 3. The ventricles are contracting, reducing the volume of
the chamber
• 4. 60/0.8 = 75 beats per minute
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Plenary
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- Answers on whiteboards!!!!
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