HEART PHYSIOLOGY I Flashcards
what does it mean by saying the heart is 2 pumps that lie ‘in series’?
- equal blood flow from all organs –> right atrium –> right ventricle –> lungs –> left atrium –> left ventricle –> all organs –> back to heart as a closed cycle
- right and left pumps contract simultaneously
- atria contracts first, ventricles contract second
- valves open/close to direct blood
which circuit has a lower pressure?
pulmonary circuit has lower pressure than systemic (however same bloodflow)
how does the circulatory system modulate to fix the different in pressure but same bloodflow require in the 2 circuits?
pulmonary circuit has lower resistance
what is the y-axis in the blood pressure trace?
arterial pressure (mmHg)
what is the x-axis of the blood pressure trace?
time (s)
which phase is longer in a heart cycle, diastole or systole?
diastole
what is the highest point and lowest point of the blood pressure trace?
- highest point = systolic pressure
- lowest point = diastolic pressure
what is the pulse and the mean pressure of a blood pressure cycle?
- pulse pressure = difference between highest and lowest points
- mean pressure = average across the full cycle
what is high blood pressure called?
hypertension
what is low blood pressure called?
hypotension
what is a complication of hypotension?
syncope - fainting
what stimulates the cardiomyocyte contraction?
an increase in [Ca2+] and released in sarcoplasmic reticulum
what does calcium release mean?
myosin can bind into actin to form cross-bridges –> myosin pulls actin to shorten sarcomere and generate force
what happen to myocyte during each heartbeat?
every myocyte activated during each heart beat
how can we increase force of contraction?
- increase of cytosolic Ca2+ level
- increase the number of cross-bridge formed (since extent of cross-bridges formed is not maximised at rest)
during cardiac relaxation, how is cross-bridge release?
- decrease in cytosolic Ca2+ lvl –> Ca2+ pumped back into SR
- ATP binds to myosin
- all cardiac myocytes relax each beat
how does a contraction of 1 cardiomyocyte would help also contract the next?
- cardiac cells are connected by intercalated discs
- cardiomyotyes are also connected by gap junction which directly connects the cytoplasm –> current moves between adjacent cells
define diastole and systole?
- diastole is the relaxation phase associated with falling ventricular pressure and takes up 2/3 of the cardiac cycle
- systole is the contraction phase associated with rising ventricular cycle and takes up 1/3 of the cardiac cycle
what are the 5 main stages of a cardiac cycle?
1/ ventricular filling
2/ atrial contraction
3/ isovolumetric contraction
4/ ventricular ejection
5/ isovolumetric relaxation
- back to ventricular filling
this is a reminder to learn the cardiac cycle and put it all in together as well as associate the stages with diastole, systole and ECG (from lecture 8 and 9)
what is ECG?
waveform produced from the electrical events activity of the heart
what are the main waves/complex waves of an ECG diagram?
- P wave
- QRS complex
- T wave
what cause P wave?
atrial depolarisation (AP starts at SA node depolarise the atria)
what happens at QRS complex?
ventricular depolarisation + atrial repolarisation
what cause T wave?
ventricular repolarisation
compare the electrical and contractile cells of the heart?
- electrical: ‘pale’ striated appearance with low actin and myosin, takes up 1% of the heart’s cell
- contractile: striated appearance with high actin and myosin, takes up 99% of the heart’s cell
how does action potential propagate along the surface membrane of electrical and contractile cells?
- intercalated discs connect most cells of the heart
- gap junctions between electrical and contractile cells, as well as between contractile cells with each other –> allow current flow –> functional syncytium
what does it mean by saying functional syncytium?
millions of cardiac cells to behave as one
what are the 6 associated structures in the conduction pathway
- SA node
- interatrial bundle
- Av node
- internodal bundles
- av bundle –> left and right branch of the av bundle
- purkinje fibres
this is a reminder to learn the excitation and conduction pathway of the heart (from lecture 9)
what does SA node do?
emit signal that instruct the heart to beat
why does AV node delay the impulse
allow atria to contract and pump blood into ventricle then relax and allow ventricle to contract
why does conduction signal travel down to the bottom of the heart and then back up the ventricular walls?
- efficient pump of bloodflow
- exit routes of the blood is at base of heart –> pump to apex and pump up from the bottom
name the 6 stages of excitation
1/ atrial depolarization, initiated by SA node –> cause P wave
2/ atrial depolarization completed, impulse delayed at AV node
3/ ventricular depolarization begins at apex –> cause QRS complex, at the same time atrial repolarization occurs
4/ ventricular depolarization complete
5/ ventricular repolarization begins at apex –> cause T wave
6/ ventricular repolariztion complete
this is a reminder to learn the whole diagram on lecture 9 and try to explain it all in one, as well as define the heart event during lubb and dupp sound
what structure is also known as the pacemaker of the heart?
SA node
what directly stimulate function at purkinje fibres?
sympathetic cardiac nerves
