Transcript The cardiac cycle

The cardiac cycle
Describing the sequence of
events in one heart beat
Learning Intentions
Describe the cardiac cycle with reference
to the action of the valves in the heart
Introduction
It is important that the chambers of the
heart contract in a coordinated fashion.
The sequence of events involved in one
heartbeat is called the cardiac cycle.
Definitions
Systole = period of ventricular contraction.
Diastole = period of ventricular relaxation.
NOTE: Normally diastole is longer than
systole.
Cardiac cycle
 General Principles.
 Contraction of the myocardium generates
pressure changes which result in the orderly
movement of blood.
 Blood flows from an area of high pressure to an
area of low pressure, unless flow is blocked by
a valve.
 Events on the right and left sides of the heart are
the same, but pressures are lower on the right.
Atrial systole
 The heart is full of blood
and the ventricles are
relaxed
 Both the atria contract
and blood passes down
to the ventricles
 The atrio-ventricular
valves open due to blood
pressure
 70% of the blood flows
passively down to the
ventricles so the atria do
not have to contract a
great amount.
Ventricular systole
 The atria relax.
 The ventricle walls
contract, forcing the
blood out
 The pressure of the
blood forces the atrioventricular valves to
shut (producing the
heart sound ‘lub’)
Ventricular systole
 The pressure of
blood opens the
semi-lunar valves.
 Blood passes into
the aorta and
pulmonary arteries.
Diastole
 The ventricles relax
 Pressure in the ventricles
falls below that in the
arteries
 Blood under high
pressure in the arteries
causes the semi lunar
valves to shut. This
produces the second
heart sound, ‘dub’.
 During diastole, all the
muscle in the heart
relaxes.
 Blood from the vena
cava and pulmonary
veins enter the atria.
 The whole cycle
starts again.
Pressure changes during one heart
beat
Atrial
Systole
Ventricular
Systole
Diastole
“DUB”
“LUB”
Cardiac cycle
= 0.8 sec
60/0.8 bpm
= 72 bpm
A
Atrioventricular (bicuspid / mitral) valve(s) closes (“snaps shut”– makes 1st
louder heart sound “LUB”
B
Semilunar valve(s) (aortic valve) opens
C
Semilunar valve(s) closes – makes second softer heart sound “DUB”- shut
due to blood accumulating in their pockets
D
Atriioventricular (bicuspid) valve(s) opens
Cardiac cycle
Match the letter on the graph to the following
events
semilunar (aortic) valve starting to open
atrio-ventricular (bicuspid) valve about to open
semilunar (aortic) valve about to close
atrio-ventricular (bicuspid) valve about to close
left ventricle starting to contract
both left atrium and left ventricle relaxing
minimum blood volume in left ventricle
key
B
16
14
aorta
left ventricle
left atrium
A
12
10
8
H
blood 6
pressure
/ kPa 4
G
2
F
E
C
0
–2
D
0
time / s
0.80
Length of 1 cardiac cycle ~ 0.8 sec
No of beats per minute = 1 x 60/0.8 sec = 75 beats/min