HEART PHYSIOLOGY I

Question 1

what does it mean by saying the heart is 2 pumps that lie ‘in series’?

Answer 1

• 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

Question 2

which circuit has a lower pressure?

Answer 2

pulmonary circuit has lower pressure than systemic (however same bloodflow)

Question 3

how does the circulatory system modulate to fix the different in pressure but same bloodflow require in the 2 circuits?

Answer 3

pulmonary circuit has lower resistance

Question 4

what is the y-axis in the blood pressure trace?

Answer 4

arterial pressure (mmHg)

Question 5

what is the x-axis of the blood pressure trace?

Answer 5

time (s)

Question 6

which phase is longer in a heart cycle, diastole or systole?

Answer 6

diastole

Question 7

what is the highest point and lowest point of the blood pressure trace?

Answer 7

• highest point = systolic pressure
• lowest point = diastolic pressure

Question 8

what is the pulse and the mean pressure of a blood pressure cycle?

Answer 8

• pulse pressure = difference between highest and lowest points
• mean pressure = average across the full cycle

Question 9

what is high blood pressure called?

Answer 9

hypertension

Question 10

what is low blood pressure called?

Answer 10

hypotension

Question 11

what is a complication of hypotension?

Answer 11

syncope - fainting

Question 12

what stimulates the cardiomyocyte contraction?

Answer 12

an increase in [Ca2+] and released in sarcoplasmic reticulum

Question 13

what does calcium release mean?

Answer 13

myosin can bind into actin to form cross-bridges –> myosin pulls actin to shorten sarcomere and generate force

Question 14

what happen to myocyte during each heartbeat?

Answer 14

every myocyte activated during each heart beat

Question 15

how can we increase force of contraction?

Answer 15

• increase of cytosolic Ca2+ level
• increase the number of cross-bridge formed (since extent of cross-bridges formed is not maximised at rest)

Question 16

during cardiac relaxation, how is cross-bridge release?

Answer 16

• decrease in cytosolic Ca2+ lvl –> Ca2+ pumped back into SR
• ATP binds to myosin
• all cardiac myocytes relax each beat

Question 17

how does a contraction of 1 cardiomyocyte would help also contract the next?

Answer 17

• cardiac cells are connected by intercalated discs
• cardiomyotyes are also connected by gap junction which directly connects the cytoplasm –> current moves between adjacent cells

Question 18

define diastole and systole?

Answer 18

• 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

Question 19

what are the 5 main stages of a cardiac cycle?

Answer 19

1/ ventricular filling
2/ atrial contraction
3/ isovolumetric contraction
4/ ventricular ejection
5/ isovolumetric relaxation
- back to ventricular filling

Question 20

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)

Question 21

what is ECG?

Answer 21

waveform produced from the electrical events activity of the heart

Question 22

what are the main waves/complex waves of an ECG diagram?

Answer 22

• P wave
• QRS complex
• T wave

Question 23

what cause P wave?

Answer 23

atrial depolarisation (AP starts at SA node depolarise the atria)

Question 24

what happens at QRS complex?

Answer 24

ventricular depolarisation + atrial repolarisation

Question 25

what cause T wave?

Answer 25

ventricular repolarisation

Question 26

compare the electrical and contractile cells of the heart?

Answer 26

- 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

Question 27

how does action potential propagate along the surface membrane of electrical and contractile cells?

Answer 27

- 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

Question 28

what does it mean by saying functional syncytium?

Answer 28

millions of cardiac cells to behave as one

Question 29

what are the 6 associated structures in the conduction pathway

Answer 29

- SA node - interatrial bundle - Av node - internodal bundles - av bundle --> left and right branch of the av bundle - purkinje fibres

Question 30

**this is a reminder to learn the excitation and conduction pathway of the heart (from lecture 9)**

Question 31

what does SA node do?

Answer 31

emit signal that instruct the heart to beat

Question 32

why does AV node delay the impulse

Answer 32

allow atria to contract and pump blood into ventricle then relax and allow ventricle to contract

Question 33

why does conduction signal travel down to the bottom of the heart and then back up the ventricular walls?

Answer 33

- efficient pump of bloodflow - exit routes of the blood is at base of heart --> pump to apex and pump up from the bottom

Question 34

name the 6 stages of excitation

Answer 34

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

Question 35

**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**

Question 36

what structure is also known as the pacemaker of the heart?

Answer 36

SA node

Question 37

what directly stimulate function at purkinje fibres?

Answer 37

sympathetic cardiac nerves