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).