EKG and the Cardiac Cycle Flashcards
Non contractile cells are called what?
Pacemakers cells (autorythmic)
Contractile cells
responsible for the heart’s pumping function
like skeletal muscle, depolarization precedes contraction
unlike skeletal muscle, action potentials in cardiac muscle cells have a characteristic hump/plateau
What is most of the heart made up of?
Contractile cells
3 steps of cardiac action potential
- depolarization: open fast sodium (Na+) channels, extracellular Na+ enter
rising phase of action potential (-90mV to +30mV)
influx of Na+ will stop quickly
- voltage change opens calcium (Ca2+) channels, influx of extracellular Ca2+
Ca2+ influc prolongs depolarization - the plateau
cells will contract as long as Ca2+ entering
- Repolarization: results from inactivated Ca2+ channels, the opening of the potassium (K+) channels - an efflux pf K+
resting potential (-70mV) is restored
Ca2+ is either pumped out of the cell or into the sarcoplasmic reticulum
Functions of Plateau
Both the action potential and the contraction phase longer in cardiac muscle than skeletal muscle
Sustained contraction ensures efficient ejection of blood from the ventricles
Longer absolute refractory period avoids tetany
Electrocardiography
the electrical currents generated in and transmitted through the body can be detected
graphic recording of heart’s cavity
has 3 distinguishable waves or deflections
P Wave
Last .08s
Results from movement of the depolarization waves from SA to AV Node
the atria contract .1s after the P Wave begins
QRS Complex
Last .08s
Results from ventricular depolarization, precedes ventricular contraction
T Wave
Last .16s
Results from ventricular repolarization
When does atrial repolarization occur?
During ventricular depolarization - the resultant wave was obscurred by the QRS complex
Interval
duration of time that includes 1 segment and 1+ wave
Segment
region between two waves
P-R interval
.16 s - the beginning of atrial depolarization to the beginning of ventricular depolarization
S-T segment
action potentials of ventricular myocytes are in plateau, the entire ventricular myocardium is depolarized
an elevated or depressed ST segment can indicate cardiac ischemia
Atrial Depolarization
Completed by SA Node, causes P Wave
Atrial Depolarization Complete
impulse delayed at Av Node
Ventricular Depolarization
begins at apex, causes QRS complex
atrial repolarization occurs, but is obscurred
Ventricular repolarization
begins at apex, causes T Wave
the cardiac cycle is … events of the heart
mechanical
Systole
contraction
blood is forced out of the heart’s chamber
Diastole
relaxation
blood refills the heart’s chambers
Steps of cardiac cycle
- Vetricular filling:
- pressure is low, blood flows from atria to vetricles
- AV valves are open, SL valves are closed
- responsible for 80% of ventricular filling
- following atrial depolarization (P Wave), atrial systole occur, and blood is compressed into the ventricles
- end diastolic volume (EDV): the maximum volume of blood that the ventricles will contain the cardiac cycle
- atrial diastole and the start of the ventricular depolarization
cardiac cycle step 2 (Isovolumetric contraction)
- atria relax slide 16 + 17
flow of blood through the heart is governed by …
pressure changes - blood always follows down a pressure gradient (high -> low)
restarting the cardiac cycle
while the ventricles are contracting in systole, the atria are diastole and filling
when the pressure in the filling atria exceeds the pressure in the ventricles, the AV valves open, and ventricular filling begins again
1 cardiac cycle - .8s
atrial systole - .1s
ventricular systole - .3s
quiescent period - .4s
Pulmonary Circulation
low pressure circuit - pressure in the pulmonary arteries = 24/20 mmHg
Systemic circulation
higher pressure circuit - pressure in the aorta = 120/80 mmHg
both sides of the heart eject…
the same volume of blood with each beat
How many sounds are heard with each heartbeat?
two sounds
1st sound
Av valves closing
- start of ventricular systole
- longer, louder sound
2nd sound
AL valves closing
- start of ventricular diastole
- shorter, sharper sound
Murmur
abnormal heart sound secondary to turbulent blood flow
more common in children and elderly people; thin walled hearts allow more vibration
can indicate of a valve problem - insufficient or incompetent valves allowing regurgitation or back flow
