Cardiac Cycle

Question 1

cardiomyocytes

Answer 1

heart muscle cells

Question 2

intercalated discs

Answer 2

connect cardiomyocytes and allow coordinated contraction

Question 3

what organelle are cardiomyocytes rich in

Answer 3

mitochondria - lots of ATP required for continuous contractions

Question 4

right vs left ventricle

Answer 4

right - thinner myocardium , large lumen

left - thick myocardium, generates much greater BP to overcome aortic pressure

Question 5

what are the two AV valves

Answer 5

between atria and ventricles
tricuspid (right)
bicuspid (left) also known as mitral
LAB RAT

Question 6

when do the AV valves open

Answer 6

when pressure in the atria exceeds that of the ventricles, forced closed when ventricular pressure higher than atria

Question 7

what are the two semi lunar valves called

Answer 7

right - pulmonary valve
left - aortic valve
between ventricles and artery

Question 8

papillary muscles

Answer 8

projections of the ventricular walls that fasten AV valves to ventricular walls preventing there movement therefore preventing backflow of blood

Question 9

chordinae tendineae

Answer 9

fibrous connective tissue (heart strings) that connect papillary muscles to the valve cusps

Question 10

valve regurgitation

Answer 10

valves not closed tightly so blood leaks back into chambers

Question 11

valve stenosis

Answer 11

stiffening of valve cusps so valves dont open fully therefore insuffcient blood flow

Question 12

end diastolic volume

Answer 12

volume of blood in ventricle prior to contraction

Question 13

end systolic volume

Answer 13

volume remaining in ventricle after contraction

Question 14

how is stroke volume calculated

Answer 14

EDV - ESV

volume of blood ejected per heartbeat

Question 15

how is HR determined

Answer 15

HR determined by rate at which sino-atrial node fires action potentials.
however the autonomic NS determines the rate of APs and therefore HR

Question 16

chronotrophy

Answer 16

heart rate

Question 17

where is the SA node located

Answer 17

wall of the right atrium

Question 18

describe the path of the AP across the heart

Answer 18

1 - SA node fires
2 - excitation spreads through atrial myocardium initiating atrial contraction
3 - AV node fires
4 - impulse spreads down bundle of HIS which then splits into left and right bundle branches
5 - then spreads to purkinje fibres which distributes excitation through ventricular myocardium

Question 19

describe how action potentials are generated at the SA node

Answer 19

1 - leaky Na channels allow slow Na influx (pacemaker potential)
2 - once threshold reached voltage gated Ca+ channels open allowing Ca into the cell
3 - at peak Ca channels close and K+ channels open allowing K+ to leave cell causing rapid hyperpolarisation

Question 20

describe ventricular action potentials

Answer 20

1 - rapid depolarisation - via fast Na channels and slow Ca channels
2 - early repolarisation - at peak Na channels close and K+ channels open
3 - plateau phase - K+ efflux is balanced by Ca influx
4 - repolarisation - Ca channels close and K+ efflux dominates

Question 21

what do ECGs detect

Answer 21

electrical activity of the heart

Question 22

P wave

Answer 22

shows atrial depolarisation

Question 23

QRS wave

Answer 23

shows ventricular depolarisation

Question 24

T wave

Answer 24

shows ventricular repolarisation

Question 25

S-T interval

Answer 25

plateau phase of ventricular contraction

Question 26

P-R interval

Answer 26

delay through AV node

Question 27

how is cardiac output calculated

Answer 27

CO = SV x HR

Question 28

what does starlings law state

Answer 28

the more the muscle is stretched in response to the filling of the heart chambers the greater the force of contraction

Question 29

cardiac preload

Answer 29

stretch of cardiomyocytes prior to contraction

Question 30

cardiac afterload

Answer 30

pressure heart must eject blood against