Cardiac Cycle Flashcards
phases of a non-nodal action potential
phase 0: depolarization (Na entry)
phase 1: rapid repolarization (transient K exit)
phase 2: plateau (Ca entry and K exit)
phase 3: repolarization (K exit)
phase 4: resting membrane potential (Na/K pump and K leaking)
what is excitation contraction coupling
process of AP arrival leading to myofibril contraction and relaxation
myofibrils
actin and myosin
actin: thin filament
myosin: thick filament
sarcomere
functional unit of contraction
cross-bridge cycling
ATP dependent process of actin and myosin sliding to shorten the sarcomere
begins with Ca influx
actin-troponin complex
tropomyosin fiber wraps around actin and covers the myosin head binding site on the actin –> prevents myosin binding
Ca must bind to troponin to cause tropomyosin to move off of myosin binding site
troponin C
binding site for Ca on troponin complex
troponin I
inhibits actin-myosin interaction by blocking the binding site
troponin T
binds troponin complex to tropomyosin
tropomyosin
supports actin and regulates interactions with myosin
L type Ca channels
transports Ca from extracellular –> intracellular
opens in response to changes in membrane potential
ryanodine receptors
transports Ca from sarcoplasmic reticulum to cytosol
opens in response to Ca influx from L type channels
what is the main source of Ca used for contraction
sarcoplasmic reticulum
SERCA
sarco-endoplasmic reticulum ATPase
transports Ca from cytosol back into the SR during recovery to allow for relaxation
phospholamban
inhibits SERCA to slow down rate of relaxation –> ultimately slows HR and contractility
PMCA
plasma membrane Ca ATPase
transports Ca from intra –> extracellular
Na/Ca exchanger
transporters Ca from intra –> extracellular
steps of contraction and relaxation of myocytes
- cell depolarizes from opening of Na channels (phase 0)
- extracellular Ca enters through L-type Ca channels (phase 2)
- intracellular Ca triggers Ca release from SR via ryanodine receptors
- increased cytosolic Ca –> binds troponin C –> pulls tropomyosin off of myosin binding site
- actin-myosin cross bridging occurs to cause contraction
- SERCA sequesters Ca back into SR
- myocyte relaxes
what two factors affect contractility
Ca concentration
Ca sensitivity
what mediators and receptors are used in sympathetic stimulation of EC coupling
NE and epi
B1 adrenergic receptors
effects of sympathetic stimulation on EC coupling
phosphorylation of:
1. L-type channels: phosphorylation increases Ca influx
2. Phospholamban: when phosphorylated, decreases SERCA inhibition –> increased rate of relaxation
3. troponin I –> increases rate of relaxation
NET: increased chronotropy, inotropy, dromotropy, and lusitropy
what mediator is used in parasympathetic stimulation of EC coupling + effects
acetylcholine
NET: decreases chronotropy, inotropy, dromotropy, and lusitropy
what is the cardiac cycle
sequence of mechanical and electrical events that occur during each heart beat
what initiates the cardiac cycle
SA node
systole
contraction and emptying
AV valves: closed (prevent backflow)
SL valves: open
diastole
relaxation and filling
AV valves: open
SL valves: closed
phase 1 of cardiac cycle
atrial contraction
occurs at end of diastole to “top off” the ventricles
AV: open
SL: closed
pressure during phase 1 of cardiac cycle
atrial = ventricular
sounds heard during phase 1 of cardiac cycle
S4 sound
normal in LA, abnormal in SA
phase 2 of cardiac cycle
isovolumetric contraction
occurs at start of systole to generate enough pressure to open SL valves
AV: closed
SL: closed
pressure during phase 2 of cardiac cycle
end diastolic volume
large increase in ventricular pressure
small increase in atrial pressure
sounds during phase 2 of cardiac cycle
S1 sound - closing of AV valves
normal in all animals
phase 3 of cardiac cycle
rapid ejection
occurs during systole to push blood out of ventricles
AV: closed
SL: open
pressure during phase 3 of cardiac cycle
ventricular = aortic pressure
then ventricular pressure decreases as blood exits
sounds during phase 3 of cardiac cycle
no sound
any sounds heard = flow murmur
phase 4 of cardiac cycle
reduced ejection
occurs during end of systole to finish contraction via passive flow
AV: closed
SL: open
pressure during phase 4 of cardiac cycle
aortic pressure slightly > ventricular pressure
both are decreasing
atrial pressure increases slightly as it continues to fill (venous return)
sounds during phase 4 of cardiac cycle
none
phase 5 of cardiac cycle
isovolumetric relaxation
occurs during early diastole to begin active ventricular relaxation
AV: closed
SL: closed
pressure during phase 5 of cardiac cycle
end-systolic volume
ventricular < aortic pressure to cause SL valve closure
increase in atrial pressure
sounds during phase 5 of cardiac cycle
S2 sound - closure of SL valves
normal in all species
phase 6 of cardiac cycle
rapid/early filling
occurs during diastole to allow for rapid ventricular filling/atrial emptying
PASSIVE process - majority of filling
AV: open
SL: closed
pressure during phase 6 of cardiac cycle
atrial pressure > ventricular pressure
sounds during phase 6 of cardiac cycle
S3 sound
normal in LA, abnormal in SA
windkessel effect
aortic/arterial blood flow continues even during diastole
aortic walls stretch during systole to store blood; walls contract during diastole to maintain organ perfusion
phase 7 of cardiac cycle
reduced filling (diastasis)
occurs during diastole; blood flow from atria to ventricles nearly stops
AV: open
SL: closed
pressure during phase 7 of cardiac cycle
atrial pressure slightly > ventricular pressure
mostly done filling at this point - rest occurs during phase 1
sounds during phase 7 of cardiac cycle
none
wiggers diagram
diagrams the change in atrial, ventricular, and aortic pressure during the cardiac cycle
diagram is the same shape of the curve for R and L sides of the heart BUT right is at lower pressures
how does right side stroke volume compare to left side stroke volume
equal - same amount of blood gets ejected
how does right side pressure compare to left side pressure
right side < left side
what does AV valve closure define
the start of systole
what does SL valve closure define
the start of diastole
what is stroke volume
the volume of blood ejected from the ventricle in one cardiac cycle
SV = EDV - ESV
EDV: end-diastolic volume (greatest ventricular volume)
ESV: end-systolic volume (lowest ventricular volume)
what is ejection fraction
the percentage of blood leaving the ventricle with each cycle
EF = SV / EDV
OR
EF = (EDV - ESV) / EDV
