The Cardiac Cycle Flashcards
What are the 3 cations that are heavily involved in the cardiac cycle?
- Na+
- K+
- Ca2+
There are 2 types of K+ channels that are involved in the cardiac cycle action potential. What is the inward rectifier K+ channel?
- opens at rest to maintain resting membrane potential (Vm)
- INWARD RECTIFIER is open leaking K+
- K+ leaking out keep Vm below -70mV
There are 2 types of K+ channels that are involved in the cardiac cycle action potential. What is the delayed rectifier K+ channel?
- K+ channel that opens to facilitate depolarisation
- all gating occurs with a delay
During a normal cardiac cycle, which cation begins to increase the Vm towards 0mV?
- Na+
Once Na+ has increased sufficiently during a normal cardiac action potential the cell is to commited to an all or nothing action potential. What is the name given that the current has to pass to initiate depolarisation, and roughly what voltage is this?
- threshold (around -50mV)
- depolarisation reaches around +30mV
Once the action potential of a cardiomyocyte has completed, what is the term given to the cell that occurs directly following depolarisation?
- repolarisation
What happens to Na+ and K+ channels during repolarisation?
- Na+ channels close
- delayed rectifier K+ channels open
- Vm becomes negative again
Once the cardiomyocyte has undergone repolarisation, there is a point where is goes below the resting Vm, what is this called?
- refractory period
Once the cardiomyocyte has undergone repolarisation and the membrane has dropped below the resting Vm, called the refractory period, which channel opens to restore Vm?
- inward rectifier K+ channels
- K+ slowly released
During the refractory period are cardiomyocytes able to recieve another acton potential?
- no
- refactory means no electrical impulse
- allows the heart to refil
During the refractory period cardiomyocytes are not able to recieve another acton potential. Multiple action potentials, as those found in the muscle is called tatanus, which is what is found in skeletal muscle. Why is it important that cardiac tissue does not undergo tetanus?
- to ensure adequate filling time for the heart between contractions
How many phases are there in normal ventricular myocyte action potentials?
- 5
- from 0 - 4
What happens during phase 0 of ventricular myocyte action potential?
- depolarisation due to Na+ entering myocyte
What is the positive feedback loop that occurs during phase 0 of the ventricular myocyte action potential?
- Na+ channels open intially during depolarisation
- once Vm reaches threshold more Na+ channels open
- so voltage is the positive feedback
What happens during phase 1 of ventricular myocyte action potential?
- delayed rectified K+ channels open
- K+ leaves cell causing small drop in charge
What happens during phase 2 of ventricular myocyte action potential?
- Ca2+ channels open
- Ca2+ entering and K+ leaving causes a plateau
What happens during phase 3 of ventricular myocyte action potential?
- rapid repolarisation
- Ca2+ channels close
- K+ continue to leaves myocyte
What happens during phase 4 of ventricular myocyte action potential?
- no hyperpolarisation
- resting Vm returns
- inward rectifier K+ opens and K+ leaks out to maintain Vm
Do action potential from the sinus and atrioventricualr nodes have inward rectified K+ channels?
- no
What is the name given to channels that facilitates action potentials from SN and AV nodes?
- the if current or funny current
- mainly Na+ into the cell, but a little K+ out of the cell
Instead of Na+ initiating depolarisation like in cardio myocytes in phase 0, what cations initiates phase 0 in cardiac action potentials in sinus and AV nodes?
- opening of Ca2+ channels
In cardiac action potentials in sinus and AV nodes there is no phase 1 or 2. What cation channel causes repolarisation in phase 3?
- delayed rectifier K+ channel
What are hyperpolarisation activated cyclic nucleotide (HCN) gated channels?
- cells capable of generating their own rhythm
- SA and AV nodes are examples
What are intercalted discs?
- connections between myocytes
What 3 things make up an intercalated disc?
- desmosomes (structure holding cells together)
- gap junctions (ion movement)
- adherens junctions (anchor thin filaments)
Why are gap junctions important in cardiac tissue?
- allow rapid conduction of action potentials
What is a syncytium?
- a multinucleated cell
- like syncytiotrophoblast in embryology
There are 2 synctium in cardiac tissue, the atria and ventricles. Why is it important that these are seperate?
- if it was one then the heart would contract as one like skeletal muscle
There is a delay of 120-200ms when the AV node receives the action potential from the sinus node. Why is thius required?
- allows ventricles to fill before contraction
Although the sinus and AV node are able to maintain their own rhythm, what neurological system can influence this, and what are the effects of this?
- autonomic
- sympathetic = increased action potential speed
- parasympathetic = decreased action potential speed
What is starlings law?
- law stating the relationship between stroke volume and venous return
- venous return generally measured in end diastolic volume
In sterlings law, venous return (preload) stretches the ventricles. What is the relationship between the number of cross bridges between actin (thin filaments) and myosin (thick filaments) and the lenght of the muscle?
- increased lenght = ⬆️ stretch of myocytes
- ⬆️ stretch of myocytes = ⬆️ number of cross bridges
- increased muscle lenght and crossbridge = ⬆️ force generation
- increased muscle lenght and crossbridge = ⬆️ duration of contraction
What is an example of intrinsic and extrinsic regulation of contractile force in cardiac tissue?
- intrinsic = starling mechanism
- extrinsic = sysmpathetic stimulation
Intrinsic regulation of contractile force of cardiac tissue is dependent on starlings law. As the number of cross bridges increase as the muscle is stretched what happens to the force and duration of the muscle contraction?
- increased force generation
- increased contraction duration
Extrinsic regulation of contractile force of cardiac tissue is dependent on sympathetic stimulation. As the number of cross bridges does not change, what happens to the force and duration of the muscle contraction?
- increased force generation
- similiar duration of force generation as HR increases so duration cannot increase as well
- faster and stronger contraction
When looking at the cardiac cycle below it shows a single beat of the heart. What does the peak and the plateau of the cardiac cycle relate to?
- plateau along the bottom = diastolic
- peak = systolic
When looking at the cardiac cycle below it shows a single beat of the heart. If we consider this to be from the left ventricle at what point in the image would the mitral valve open and close?
- mitral valve opens at end of systolic = bottom right
- mitral closes at end of diastolic = bottom left
When looking at the cardiac cycle below it shows a single beat of the heart. If we consider this to be from the left ventricle at what point in the image would the aortic valve open and close?
- aortic valve opens at start of systolic. Valve opens as pressure in left ventricle exceeds aortic pressure
- aortic valve closes at end of systolic. Valve closes as pressure in left ventricle is below aortic pressure
When looking at the cardiac cycle below it shows a single beat of the heart. If we consider this to be from the left ventricle, where would isovolumetric contraction occur and what is this?
- occurs between mitral valve closing
- before aortic valve opens
- blood cannot leave but pressure increases
When looking at the cardiac cycle below it shows a single beat of the heart. If we consider this to be from the left ventricle, where would isovolumetric relaxation occur and what is this?
- after aortic valve closes
- before mitral valve opens
- blood remaining cannot go anywhere so volume remains
When looking at the cardiac cycle below it shows a single beat of the heart. If we consider this to be from the left ventricle, at what point would blood be pumped out of the heart on the figure?
- in systolly
- between aortic valve opening and closing
When looking at the cardiac cycle below it shows a single beat of the heart. If we consider this to be from the left ventricle, what are the 3 stages that occur once the mitral valve has opened and before the atria contract again?
1 - passive filling
2 - diastasis
3 - active filling
At what point in the figure below would you hear the 2 sounds of the heart, referred to as S1 and S2 and what happens at each one?
- S1 = mitral valve (and tricuspid valve) closing
- S2 = aortic valve (and pulmonary valve) closing
When looking at the cardiac cycle below it shows a single beat of the heart. If we consider this to be from the left ventricle, what happens to the LV volume in systolic and diastolic?
- LV progressively decreases in systolic as blood is pumped out
- LV progressively fills during diastolic
What is the name given to the plots where all the cardiac cycle data is put onto the same plot?
- Wiggers plots
What is a left ventricle pressure volume loop?
- a plot that represents one heart beat
- plot includes volume and pressure of LV
- includes systolic and diastolic
In the left ventricle volume pressure loop where would you expect to find the following:
a = isovolumic contraction
b = ejection
c = isovolumic relaxation
d = diastolic filling
a = isovolumic contraction is right verticle
b = ejection is curved line at top
c = isovolumic relaxation is left verticle line
d = diastolic filling is line on bottome
In the left ventricle volume pressure loop where would you expect to find the following:
a - aortic valve opens
b - aortic valve closes
c - mitral valve opens
d - mitral valve closes
- a - aortic valve opens - top right corner
- b - aortic valve closes -top left corner
- c - mitral valve opens - bottom left corner
- d - mitral valve closes - bottom right corner
What is the most accurate marker for a myocardial infarction that is released into the blood when cardiac muscle is damaged?
- cardiac troponin T or I
- specific to cardiac muscle
Although not specific as troponin T or I, there is an enzyme that can be useful for identifying if a patient has has a myocardiac infarction. What is this called?
- creatine kinase-MB (CK-MB)
- creatine kinase is found throughout body
- CK-MB is specific to cardiac tissue
