- Slides: 6
Key Revision Points for Cardiac Function
Key points about the cardiac cycle �SAN is the heart’s pacemaker – intrinsic rhythm. �Impulses spread through the atria causing contraction of both atria. �Impulse picked up by AVN. �Impulse spreads through septum in the bundle of His. �Impulse then spreads through ventricles in Purkinje fibres causing ventricular contraction.
Key points about regulation of heart rate �SAN rate is altered by autonomic nervous system. �Parasympathetic vagus nerve slows heart rate. �Sympathetic nerve speeds up heart rate. �Release of adrenaline increases heart rate prior to exercise.
Key points about increasing heart rate �During exercise there is an increase in carbon dioxide levels. �This causes an increase in the acidity of blood. �This is detected by chemoreceptors. �Impulses sent from medulla in the brain. �Decreases vagus stimulation. �Increases sympathetic impulses. �Results in an increase in activity from SAN and an increase in heart rate.
Key points about the effects of exercise on the heart (short term) �Heart rate increases. �Stroke volume increases. �This is due to Starling’s Law. �Cardiac output increases. �Remember: SV x HR = cardiac output
Key points about the effects of training on the heart (long term) �Cardiac hypertrophy. �Results in increase in stroke volume. �RESTING heart rate decreases. �RESTING cardiac output remains the same (no need for resting levels to change).