CARDIAC SYSTEM

1. CARDIAC SYSTEM

2. Starter – From Homework Write down a definition for the following • Stroke Volume • Heart Rate • Cardiac Output • Starling’s Law Add equations where necessary

3. TODAY L/O To identify and understand the 3 areas of the cardiac system • Stroke Volume • Heart Rate • Cardiac Output

4. Stroke Volume The amount of blood pumped out by the left ventricle in each contraction. On average the resting stroke volume is around 70ml

5. 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

6. 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 Bradycardia is when your HR Is below 60bpm

7. 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 100-220ml

8. Work out these Equations • SV = 100 HR = 100 Q = ? • SV = 95 HR = 60 Q = ? • SV = 80 HR = ? Q = 3200 ml/min • SV = 60 HR = ? Q = 7200 ml/min • SV = ? HR = 180 Q = 12600 ml/min • SV = ? HR = 80 Q = 6800 ml/min

9. Work out these Equations • SV = 100 HR = 100 Q = 10000 ml/min • SV = 95 HR = 60 Q = 5700 ml/min • SV = 80 HR = 40 Q = 3200 ml/min • SV = 60 HR = 120 Q = 7200 ml/min • SV = 70 HR = 180 Q = 12600 ml/min • SV = 85 HR = 80 Q = 6800 ml/min

10. 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.

11. 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.

12. 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 non- essential organs • Closing/vasoconstriction of precapillary sphincters supplying non essential organs

13. How can Cardiac Output increase during exercise? • Increase in heart rate • Increase in stroke volume • Adrenaline released • 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

14. 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%