Topic 9 - Cardiac cycle Flashcards
(16 cards)
What are the 2 main phases of the cardiac cycle?
- Systole = Ventricle contracts & pumps blood out (0.3sec)
- Diastole = Ventricle relaxes & fills with blood (0.5sec)
Where is the junction that the action potential has to reach to get to the ventricles?
Atrio-ventricular node = gateway to ventricles
Located at bottom right atrium
*Note: Action potential goes all the way down to the bottom of the heart to contract muscles
What occurs mechanically when the action potential starts?
- The heart is filling up with blood
- As the action potential moves, the atria are contracting (just b/f ventricles)
What is a heart attack?
- Blood supply to muscular wall of ventricle is stopped.
- It is caused by fatty deposits in the coronary artery
What are baroreceptors?
They help to regulate heart function
What are the 5 mechanical phases of the cardiac cycle?
- Ventricular filling (diastole)
- Atrial contraction (diastole)
- Isovolumetric ventricular contraction (systole)
- Ventricular ejection (systole)
- Isovolumetric ventricular relaxation (diastole)
How does blood get back to heart?
- Skeletal muscle contraction
- Blood is in veins
- Skeletal muscle contracts and pushes blood through open valve.
- When skeletal muscles contract, valves are closed to prevent backflow - Breathing
- increase pressure in veins -> move blood back to heart
What are the stages of the electrical events in the cardiac cycle?
- Initiation & then spread of AP
- AP initiated by pacemaker cells at sinoatrial node.
- AP spreads by “gap junctions” in atrium - Spread of excitation to ventricles via atrioventricular (AV) node
- AV node only electrical gateway b/w atria & ventricles
- Responsible to slow signal to ventricle as has slight more neg. rest mem. pot.
*slow signal allows atria finish contraction - Activation of ventricles
- AP moves into bundle of His, then to bundle branches
- Then move to Purkinje fibres & then activates cardiomyocytes
Why do Pacemaker cells not have a phase of no AP’s allowed? How do their AP’s work?
- They have a slow depolarisation phase
- As soon as repolarisation occurs, channels triggered by it and cause Na+ & Ca2+ into cell.
- Threshold passing results in fast Ca2+ open & Ca2+ influx, resulting in AP.
What are the 2 main cellular mechanisms enable AP spread?
- Gap junctions = cell-to-cell movement of AP where e- charge move through gap junctions (channels) to activate next-door cell
- Fast conduction fibres = allow AP quick move from AV node to ventricles
What is an electrocardiogram (ECG)?
A recording of the electrical activity of the heart
What is sinus bradycardia and sinus tachycardia?
- Sinus bradycardia = heart rate too slow - less 60bpm
- Sinus tachycardia = heart rate too fast - more 100bpm
What is Cardiac output?
The amount of blood ejected by each ventricle per min.
What is the equation for Cardiac output?
Cardiac output = Heart Rate x Stroke volume
The higher work load=
- The higher the heart rate
- The lower the stroke volume (slower rate)
- Overall higher cardiac output to a point. (goes down after the pt)
*Note: Stroke volume = volume of blood ejected by left ventricle in L
What nervous system regulates the heart?
Autonomic N.S
- Sympathetic increase HR in fight/flight mode (releases adrenaline/noradrenaline -> activate Beta1-adrenoceptors on pacemaker cells)
- Parasympathetic decrease HR in rest/digest mode (release ACh -> activate muscarinic M2 receptors on pacemaker cells)
What are the 3 key factors that stroke volume is determined by?
- How much blood ventricles contain at end of diastole
- How hard heart contracts
- How much pressure the heart is pumping against (pressure in arteries)
