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Settler
Describe the route a blood cell would take
around the body. You have just left the body
entering the heart through the Vena cava.
You could do this in bullet points on
whiteboards
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 heart
• Heart muscle does not need to be stimulated by a
nerve before it will contract. The heart beat
originates in the muscle itself and, for this reason, it
is described as being myogenic.
• There are 2 phases to the beating of the heart:
– Contraction (systole)
– Relaxation (diastole)
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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Cardiac cycle
• Cardiac cycle - narrated.swf
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Cardiac Cycle: Summary
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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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Heart Rate –beats/min
Purkyne
Tissue
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Control of Heartbeat
• Cardiac muscle is
myogenic – naturally
contracts & doesn’t
need to receive
impulses
• Need to coordinate
contractions with
pacemaker = sinoatrial node (SAN)
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1. The SAN sends waves of
electrical activity which spread
through the muscle of the
atria, causing it to contract.
(Blood is forced into ventricles)
ATRIAL SYSTOLE
4. The atria relax (atrial
diastole), blood enters the
atria from the pulmonary veins
or vena cava
5. The ventricles relax
(ventricular diastole). Bicuspid
and tricuspid valves open and
blood enters the ventricles
from the atria
•Describe how heart action is
coordinated with reference to
the sinoatrial node (SA),
atrioventricular node (AVN)
and Purkyne tissue (Grade C
–B)
2. The waves of
electrical activity reach
the AVN . Here there is
a slight delay-making
sure the atria have
emptied before
ventricles contract
3. AVN passes activity
onto the bundle of His,
and these muscle fibres
conducted the waves of
excitation along the
Purkyne fibres. Once the
impulses reach the walls
of the ventricles they
cause the muscles to
contract, forcing blood out
of the heart
VENTRICULAR SYSTOLE
Cardiac Cycle: Summary
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Electrocardiograms (ECG)
Checks heart function using an electrocardiograph, it
records the electrical activity of the heart
- The heart muscle depolarises (loses electrical charge)
when it contracts, and repolarises (regains charge) when
it relaxes.
- Patches with wires are placed on the patients chest and
wires are connected to a monitor.
- Electric charges are recorded by an electrocardiograph,
as a electrocardiogram/ECG which shows the patients
normal heart rhythm.
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Electrocardiograms [ECGs]
(record the electrical activity of the heart)
The P wave is
caused by
contraction
(depolarisation) of
atria
The QRS complex is
caused by contraction
(depolarisation) of
ventricles. Larger than P
due to more muscle.
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The ST wave is caused
during ventricular
diastole. (repolarisation
of ventricles
http://anatimation.com/cardiaccycle/cardiac-cycle.html
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Terms not to be confused by
• Tachycardia – fast heart rate
• Bradycardia – a slow heart rate
• Arrhythmia – abnormal heart rhythm
•Interpret and
explain ECG
traces, with
reference to
normal and
abnormal
heart activity
(Grade B – A)
• Fibrillation – rapid contraction of heart
muscles
TASK – Identify each ECG and
explanation
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Sinus Tachycardia
Rapid fire of the SAN, the heart’s
natural pacemaker, defined as a rate
greater than 100 beats/min in an
average adult.
It’s the normal response to exercise, excitement, anxiety and also
stimulants, fever, dehydration, hypothermia & shock, hypoxia
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Bradycardia
Bradycardia occurs when the heart is beating more slowly than
fifty to sixty times a minute. The impulses that control a steady
heartbeat, are blocked, delayed, or slowed down.
It can occur as a result of age, AVN or SVN problems, metabolic
disturbances, as a result of taking certain medications, drug
abuse, or as a result of a pre-existing heart disease.
Trained athletes tend to have slow resting heart rates, and resting
bradycardia in athletes is not abnormal if no symptoms.
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Sinus Arrhythmia
The normal increase in heart rate that occurs during inspiration
(when you breathe in).
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Ventricular Fibrillation
Uncoordinated contraction of the cardiac muscle of the
ventricles in the heart. As a result, the heart fails to adequately
pump the blood,
During ventricular fibrillation, cardiac output drops to nil,
and, unless terminated promptly, death usually ensues
within minutes.
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Plenary
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- Answers on whiteboards!!!!
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Settler
Describe how the action of the heart is
initiated and co-ordinated.
In your answer you should use
appropriate technical terms, spelt
correctly.
(5 marks)
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Peer mark exam question
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Single Circulation – e.g. fish
Blood passes through heart
ONCE per complete circuit
Blood pressure reduced as blood passes through the gill
capillaries - slows down flow to the rest of the body
Limits the rate of delivery of O2 and nutrients to cells and
removal of waste
Efficient for the level of activity of fish but not mammals –
also fish do not maintain their body temperature – need to
respire relatively less compared to mammals
Double Circulation – more efficient - e.g. mammals
Heart is composed of two separate pumps – right side pumps
blood to the lungs to pick up oxygen; the blood is returned to
the left side; the left side pumps oxygenated blood rapidly and
at high pressure to the body; the blood is returned to the right
side
Blood passes through heart
TWICE per complete circuit
Higher level of activity (energy) and need to maintain their
body temperature at 370C – through respiration
Need to deliver and remove materials to and from cells rapidly
– achieved by delivering blood at high pressure to tissues.
Pulmonary – oxygenates blood & removes CO2
Systemic – oxygenated blood from lungs pumped
rapidly at an increased pressure by the heart
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