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Title: A level Biology The Cardiac Cycle
Description: power point on the cardiac cycle at a level standard
Description: power point on the cardiac cycle at a level standard
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1
...
At this time the av
valve is open and sl
valve is closed
b
...
This increases the volume of
blood in the LV
d
...
Wall of left atrium stops
contracting (atrial diastole)
and pressure falls
4
6
a
e
f
a
e
b ab 5 6
3
...
This raises the
pressure in the LV
b
...
This corresponds to QRS wave
on an ECG
c
b
e
...
Blood flows from the LV into the
aorta
g
...
4
...
a
...
Ventricular diastole is represented
by a T wave on an ECG
5
...
g
dc
d
...
When pressure in the LA
exceeds that in the LV, the av
valve opens and blood moves
from the LA to the LV
Cardiac cycle
(events on left side only –events on the right are the same but pressures
generated are less because blood is pumped a shorter distance
• 1
...
At this time the av valve is open and sl valve is
closed
– b
...
This increases the volume of blood in the LV
– d
...
Wall of left atrium stops contracting (atrial
diastole) and pressure falls
• 3
...
This raises the pressure in the LV
– b
...
This corresponds to QRS wave on an ECG
Cardiac cycle
(events on left side only –events on the right are the same but pressures
generated are less because blood is pumped a shorter distance
– d
...
When the pressure in the LV exceeds that of the
aorta, the sl valve opens
– f
...
This causes the ventricular volume to fall and
pressure in the aorta to rise
...
Wall of left ventricle stops contracting
(ventricular diastole) and pressure falls
...
Immediately pressure in LV falls below that of
the aorta and the sl valve closes to prevent flow of
blood from the aorta back into the LV
(corresponds to dub sound)
– b
...
All this time, blood has been entering the
LA from the pulmonary vein causing pressure
in the LA to rise slowly
...
When pressure in the LA exceeds that in the
LV, the av valve opens and blood moves from
the LA to the LV
Time of cardiac cycle
• On the graph, look at the time between any two
repeating points (eg atrial systole)
• The cardiac cycle on this graph is 0
...
• 1 beat
takes 0
...
8 beats
in 1 second
• 1/0
...
– It is connected to nerves but these do not
stimulate contraction but modify rate of
contraction
Co-ordination of heart beat
Co-ordination of heart beat
Contraction of heart and co-ordination
of heart beat
• In the wall of the right atrium, close to where
the vena cava enters the RA is a region of
specialised cells called
Sino-atrial node (SAN), or pacemaker
• The purpose of this is to set the rate at which
all the cardiac muscle cells contract
Contraction of heart and co-ordination
of heart beat
• The SAN generates an electrical impulse
• The impulse spreads through the cell
membranes of the cells of the atria via the
intercalated discs
• This electrical activity is identified as the P
wave on an ECG
• The impulse causes the atria to contract
...
• These fibres spread out from the base of the
ventricles and the impulses cause contraction of
both ventricles simultaneously from the base of the
ventricles
Title: A level Biology The Cardiac Cycle
Description: power point on the cardiac cycle at a level standard
Description: power point on the cardiac cycle at a level standard