Cardiac Physiology Flashcards
What is happening when the heart is in systole?
Contract & Empty
-AV valves close
-Ventricles contract, pressure builds, no volume change
-End stage AV closed pulmonary and aortic open and blood is pushed into the arteries
What is happening when the heart is in diastole?
Relax & Refilling
-From the veins, the atria fills and blood opens the AV valves, blood flows into the ventricles at the end, atria contract to push the remainder of blood into the ventricles
What is stroke volume?
End diastolic volume - end systolic volume
Why is there no change in volume during contraction?
The aortic an pulmonary and AV valves are closed = Ventricular ejection
-The blood empties into aortic and pulmonary arteries as the valve opens the AV vale stay’s closed
What is the role of the pericardial sac?
-Double walled sac, touch covering which anchors the hears, has a secretory lining with pericardial fluid providing lubrication
What are the regions of auto-rhythmicity?
SA node, AV node, Bundle of His, Purkinje Fibres
How is an action potential passed along the heart?
1) Starts at the right atria
2) AV node is the only connection of the atria to the ventricle, all pass through the AV node
3) Then goes to the Bundle of His down the septum walls, to the right and left ventricles then to the Purkinje Fibres,
=Action potential
What are the four stages of cardiomyocyte action potential?
1) Influx of Na = rapid depolarisation - K+ channels open and K+ leaves
2) Plateau - Ca2+ enters slowly into the cells
3) End of the plateau, = rapid repolarisation as K+ pumped out again
4) Resting potential until next action potential to start again
What happens to the ions during depolarisation?
–> Ca2+ in
<– K+ out
What happens to the ions during repolarisation?
Ca2+ closed
K+ open
What does an increase in cytosolic calcium do?
This comes from the extracellular space, from sarcoplasmic reticulum.
-Combines to troponin initiates cross bridge formation
What do abnormal levels of K do?
Change resting potential
-Increase or decrease results in decreased cardiac excitability and contractility.
What does an increase in extracellular K+ do?
-Rise in extracellular K reduces resting potential - depolarisation
-Inactivates Na+ channels
-Arrythmias and fatalities
What does a decrease in extracellular K+ do?
Increases resting potential (Hyperpolarisation)
-Bradycardia, cardiac rhythm abnormalities
What does changes to extracellular Ca2+ do?
*Affect membrane permeability, causing cardiac rhythm abnormalities
