coordination of cardiac cycle Flashcards
what is cardiac output
the amount of blood pumped around the body
what is the equation for cardiac output
cardiac output = stroke volume x heart rate
what is the stroke volume
-volume of blood pumped by the left ventricle each heart beat.
-typical adult at rest is 75ml
what is the heart rate
-number of time the heart beats per minute
-typical value for an adult at rest is 70bpm
what is the contraction of the myocytes called
myogenic (generate its own contraction or rhythm without the need for external nervous stimulation)
what are myocytes
muscle cells
what is initiated in the walls of the right atrium and where
-depolarisation
-in a region of the heart called the sinoatrial node
steps of how the contraction of atria and ventricles is coordinated
1) sinoatrial node initiates wave of depolarisation
2) depolarisation wave spreads over walls of atria causing atrial systole
3) slight delay at atrioventricular node
4) depolarisation travels down septum in purkyne fibres
5) start of ventricular systole at the apex of the heart
why is there a slight delay at the atrioventricular node
to allow atria to fully contract and release all blood into ventricles
what does the atrioventricular node do
-send the electrical impulse down bundle of his into ventricles via purkinjie fibres in the septum
what do electrocardiograms do
-monitor the activity of the heart
how do electrocardiograms monitor the activity of the heart
-electrodes attached to specific places on persons chest and limbs
-detect changes in electrical activity in the heart by measuring current at the skin surface and connects to a machine that draws an ECG
what is an ECG used for
-for diagnosing issues
-can be whilst relaxed or during “stress test”
what are the parts of an ECG
-P wave
-QRS complex
-T wave
what does the P wave represent
-The wave of depolarisation that spreads from the SAN across the atria causing atrial systole
what does the QRS complex represent
-The wave of depolarisation which spreads across the ventricles causing ventricular systole
what does the T wave represent
-The repolarisation of the ventricles during diastole
what’s an arrhythmia
-range of conditions where the heart beats either too fast or too slow and may be irregular or reggular
what is it called when the heart beats too fast
Tachycardia
what is it called when the heart beats too slow
bradycardia
what is ventricular fibrillation
-the absence of coordinated contraction of the ventricles caused by a chaotic electrical activity
why is ventricular fibrillation dangerous
-it can be life threating if defibrillation isnt provided
-its a type of arrhythmia
what is an artificial pacemaker
devices that are implanted in the walls of the right atrium of the heart of a person whose heart’s electrical conduction system is not working properly
what problems can an artificial pacemaker fix
-SAN not firing
-the blockage or disruption of impulses between the SAN and AVN, or in the bundle of His.
what do pacemakers do
-monitor the heart’s electrical activity and stimulate the ventricles or atria to contract when necessary.
how do artificial pacemakers stimulate the ventricles or atria to contract when necessary
Impulses are transmitted down electrodes implanted in the muscular walls.
what is the natural pacemaker
the sinoatrial node
what is the sinoatrial node responsible for
-initiating electrical impulses that regulate the hearts rhythm
-sending signals to the atrioventricular (AV) node, which then directs the electrical impulses to the ventricles
