### Cardiovascular System Lesson 2 Live Show

```CARDIAC SYSTEM
Starter – From Homework
Write down a definition for the following
•
•
•
•
Stroke Volume
Heart Rate
Cardiac Output
Starling’s Law
TODAY
L/O To identify and understand
the 3 areas of the cardiac
system
• Stroke Volume
• Heart Rate
• Cardiac Output
Stroke Volume
The amount of blood pumped out by
the left ventricle in each contraction.
On average the resting stroke volume
is around 70ml
Stroke Volume
Is determined by several factors:
Venous Return – the volume of blood
returning to the right atrium. The greater
the venous return, the greater the stroke
volume, since more blood is available to be
pumped out
The elasticity of cardiac fibres – the
degree of stretch of cardiac tissue just
prior to contraction. The greater the
stretch of the cardiac fibres, the greater
the force of contraction
Heart Rate
This is the number of complete cardiac
cycles and therefore the number of times
the left ventricle ejects blood into the aorta
per minute
The average is 72 beats per minute
Cardiac Output
• The amount of blood the heart pumps per
minute is known cardiac output (Q) (measure
in litres). From the left ventricle
• The cardiac output is a product of stroke
volume and heart rate.
• Q = SV x HR. Trained; rest 5L Exercise 34L
• HR = numbers of BPM.
• SV = amount of blood ejected from LV each
contraction (measured ml per beat).
• Measured in ml/min or L/min – Max 100220ml
Work out these Equations
1.
2.
3.
4.
5.
6.
SV = 100
SV = 95
SV = 80
SV = 60
SV = ?
SV = ?
HR = 100
HR = 60
HR = ?
HR = ?
HR = 180
HR = 80
Q=?
Q=?
Q = 3200 ml/min
Q = 7200 ml/min
Q = 12600 ml/min
Q = 6800 ml/min
Work out these Equations
1.
2.
3.
4.
5.
6.
SV = 100
SV = 95
SV = 80
SV = 60
SV = 70
SV = 85
HR = 100
HR = 60
HR = 40
HR = 120
HR = 180
HR = 80
Q = 10000 ml/min
Q = 5700 ml/min
Q = 3200 ml/min
Q = 7200 ml/min
Q = 12600 ml/min
Q = 6800 ml/min
Starling’s Law of the Heart
• Cardiac output is dependant on the amount of
venous blood returning to the right side of
the heart, otherwise known as venous return.
• During exercise, venous return increases and
therefore cardiac output increases. This is
caused by the myocardium being stretched,
resulting in the myocardium contracting with
greater force.
Starling’s Law of the Heart
• Therefore, the stimulus that causes the
greater force of contraction is the stretching
of the muscle fibres themselves.
• This relationship is known as starling’s law of
the heart.
• Intrinsic factors such as starlings law of the
heart, changes in electrolyte balance (sodium
and potassium) in the heart muscle and
increased myocardial temperature, result in
changes in heart rate.
DISTRIBUTION OF CARDIAC OUTPUT DURING EXERCISE
More blood is distributed to the working muscles.
Less blood is distributed to non-essential organs
Explanation:
• Vasodilation of arteries/arterioles supplying working
muscles/Vascular shunt
• Opening/vasodilation of precapillary sphincters
supplying working muscles
• Vasoconstriction of arteries/arterioles supplying nonessential organs
• Closing/vasoconstriction of precapillary sphincters
supplying non essential organs
How can Cardiac Output increase during exercise?
•
•
•
•
•
•
•
•
•
Increase in heart rate
Increase in stroke volume
Increase in venous return/more blood returning to the
heart
Stretches wall of right atrium which increases firing of
SA node
Greater stretching of cardiac walls increase force of
contraction/Starling’s Law
Information sent from proprioceptors/baroreceptors/
chemoreceptors to cardiac control centre (CCC)
Increase in sympathetic control
Increase in temperature which speeds up nerve impulse
Glossary
Cardiac Hypertrophy – the enlargement of the
heart due to training. Larger ventricular cavities
and thicker ventricular walls
Bradycardia – Meaning slow heart where the
resting heart rate falls below 60bpm
Ejection Fraction – the proportion of blood
actually pumped out of the LV per contraction =
SV / EDV (end diastolic fraction) = 60%
```