Cardio Misc. Flashcards
Where is the sinoatrial node located?
In the upper right atrium
What is the sinoatrial node?
It is the pacemaker of heart and site of origin of electrical excitation
How is the sinoatrial node capable of auto-rhythmicity?
As a result of pacemaker potential
What channel is responsible for pacemaker potential?
The hyper polarization activated cyclic nucleotide gated (HCN) channel
What is the process of HCN channels opening?
Following the action potential, the spontaneous opening of these channels in response to hyper polarization takes the pacemaker cells to threshold independent of a stimulus
How does action potential spread?
Via cell-to-cell conduction across gap junctions
What is the route of action potential spreading?
Atria – AV node – Bundles of His – Purkinjie fibers – Ventricles
What is the of the AV node?
It is the only point of electrical contact between the atria and ventricles
What is the role of the AV node?
To slow electrical action potential conduction between the atria and ventricles in order to allow the atria to fully contract and the ventricles fully fill before ventricular contraction
What is the resting membrane potential of ventricular myocytes?
-90mV
What is phase 0 of ventricular action potential?
Depolarization via influx of sodium
What is phase 1 of ventricular action potential?
Slight hyperpolarization due to close of sodium channels
What is phase 2 of ventricular action potential?
Plateau phase due to influx of calcium, which is responsible for calcium induced calcium release
What is phase 3 of ventricular action potential?
Hyperpolarization due to closure of calcium channels and efflux of potassium
What is phase 4 of ventricular action potential?
Resting membrane potential
What is meant by the term Chronotropic?
Increased rate of contraction
What is meant by the term Inotropic?
Modifying the force or speed of contraction of muscles
What is the parasympathetic effect on electrical activity?
Negative inotropic
What is the parasympathetic effect on electrical activity?
Positive inotropic
Where is parasympathetic innervation in the heart?
In the SA node only
Where is sympathetic innervation in the heart?
At the SA/AV nodes and ventricles
What is the parasympathetic receptor in the heart?
Muscarinic M2
What is the sympathetic receptor in the heart?
Adrenergic B1
What is the impact of the parasympathetic nervous system on the slope of pacemaker slope?
It reduces it
What is the impact of the sympathetic nervous system on the slope of pacemaker slope?
It increases it
What mediates the parasympathetic innervation in the heart?
Ach
What mediates the sympathetic innervation in the heart?
Noradrenaline
How are myocytes coupled?
Via desmosomes
How is force generated in the heart?
Via calcium and ATP dependent cross bridge cycles
Why is the plateau phase essential in ventricular potential?
It allows for calcium induced calcium release and therefore enough calcium to be present for the cross bridge cycle to occur
What is meant by the term excitation contraction coupling?
It is the physiological process of converting an electrical stimulus to a mechanical response
What is the refractory period?
It is the period in which it is not possible to produce another action potential due to inactivation of sodium channels
What is the importance of the refractory period?
Essential for preventing tetanic contraction of the heart
What is meant by the term stroke volume?
The volume of blood ejected from the heart with each beat
What is the average stroke volume?
70mls
What is the frank starling law?
It describes the mechanisms of intrinsic control of SV, stating that increasing venous return will increase stroke volume
What is afterload?
The pressure in which the heart is pumping out against
What is the relationship between the frank starling law and afterload?
The frank starling law helps to compensate for an increase in afterload, which is seen with the likes of hypertension
What mediates extrinsic control of stroke volume?
An increase in calcium-induced calcium release and contractility
What effect does the extrinsic control of stroke volume have on the frank starling curve?
It acts to shift it to the left
What is meant by the term cardiac output?
The amount of blood pumped from the heart per minute