cardiac cycle and sounds Flashcards
describe phase 4 of fast action potential?
phase 4: rest
Na,K, Ca channels are closed
cell is at resting potential
do cardiac myocytes have many funny sodium channels?
no, can’t really use them to depolarize
describe phase 0 of fast action potential?
rapid upsweep
voltage gates Na+ channels open
cell depolarizes
describe phase 1 of fast action potential?
initial repolarization
sodium channels inactivated, no Na+ enters
voltage gate k+ channels open, potassium can leave
describe phase 2 of fast action potential?
repolarization is interrupted
voltage gates Ca chanels open, calcium enters muscle cell
potassium continues to leave cell
membrane potential stabilizes at positive potential
describe phase 3 of fast action potential?
voltage gated calcium channels close
K+ channels remain open
repolarizaion completed
describe order of fast action potential phases
4,0,2,3
what cells does slow action potential occur in?
cells of conduction pathways
SA and AV nodes
describe phase 4 of slow action potential?
steady depolarization
opening of funny sodium channels
how can we alter heart rate? what part of the heart has most of these channels
how fast funny sodium channels open, SA node has the most of these channels!
thats why its the pacemaker
AV node is the backupp
describe phase 0 of slow action potential?
what is special about this?
calcium influx causes depolarization
influx is slower than Na, depolarization takes shorter amount of time
does not get as positive as in skeletal tissue
describe phase 1 of slow action potential?
initial repolarization
where is slow action potential phase 1 and phase 2 not found?
SA and AV nodal tissue
describe phase 2 of slow action potential?
calcium enters cell, allows for contraction
describe phase 3 of slow action potential?
repolarization
efflux of K+
what is P in an ECG?
atrial depolarization initiated by SA node depolarization
what is QRS in an ECG?
phase 0 depolarizations of ventricular myocytes
what is T wave in an ECG?
ventricular repolarization
Relevance of PR interval?
begin at P wave, ends at beginning of QRS wave
time it takes for depolarization to pass from atria to ventricles via AV node
what does PR interval represent, what happens if there is damage?
slow conduction velocity of AV node
damage to AV node means PR interval is prolonged
Relevance of ST interval?
end of QRS to beginning of T wave
includes no wave
amplitude gives us clinical information
Relevance of QR interval?
beginnng of QRS complex to end of T wave
includes QRS complex and T wave
total time ventricular myocytes are depolarized
what s the x axis on wiggers diagram
time in millieconds
what s the y axis on wiggers diagram
volume or pressure
expected sequence of ECG?
P wave
Pr interval
QRS complex
St segment
T wave
Isoelectric line
what does the aortic pressure line represent?
at beginning, shows aortic pressure in slow decline
-no blood being ejected
initial decline in pressure is due to movement of blood from aorta into periphery
what does aortic pressure change on ECG represent?
decline in pressure represents how fast blood moves to periphery
slow decline in aortic pressure means blood moving to periphery slowly
and vice versa
when does decline in aortic pressure end?
what is important about this point?
when pressure of ventricle opens aortic valve and blood goes into aorta
aortic pressure is measure diastolic blood pressure
aortic and ventricular pressure are close together
when does peak of aortic pressure occur, what does it represent?
systolic blood pressure
after aortic valve opens
describe dicrotic notch
blip produced by closing of aortic valve
caused by decline in aortic pressure
what does ventricular pressure curve start at?
0, pressure has to be lower than atrial so blood can come in
what happens when ventricular pressure exceeds aortic pressure?
aortic valve open, blood goes into aorta
after peak systolic pressure, what happens to ventricular pressure?
ventricle relaxes, pressure starts to decrease
when does atrial pressure increase?
shortly after p wave occurs
pushes blood into ventricle
what is isovolumetric contraction? why does it happen?
ventricular pressure causes av valve to bulge back into atria
causes atrial pressure to increase slightly
low pressure in atria, ventricular pressure causes closue of AV valve almost immediatel
takes some time to increase ventricular pressure to open AV valve
when aortic valve opens, what happens?
av valves no longer being pushed into atria
c wave ends abruptly
atrial pressure keeps increasing until what?
until AV valves open aain
during diastole and systole, compare atrial and ventricular pressures
atrial pressure is higher, allows blood to flow into ventricl
compare jugular vein pressure and atrial pressure
jugular be slightly higher so that blood can go to atria
what is end systolic volume?
blood in healthy ventricle, has about 50 ml in it
blood pressure at end of systole
when is ventricular volume at its highest?
in diastole, when blood returning to heart can flow to ventricle
what is the measurement when ventricle is full
end diastolic volume
what is isovolumic contraction?
during early phase of ventricular contraction, pressure is not changing
AV and aortic valves not open, blood has nowhere to go
what is isovolumic relaxation?
aortic/pulmonary valves close before av valves can open
ventricular volume is the same as ventricular pressure drops
what is the rapid filling phase?
ventricular pressure drops below atrial pressure
av valves open
blood from atria will go into ventricles
when does first heart sound occur
closing of AV valves
beginning of isovolumic cntraction
when does second heart sound occur
closing of aortic/pulmonic valves
dicrotic notch
when does the third heart sound occur
early in diastole
rapid filling
when does the fourth heart sound occur
blood being forced into ventricle during atrial contraction
what is diastole?
period of rest
