Cardiac Cycle

Question 1

phases of a non-nodal action potential

Answer 1

phase 0: depolarization (Na entry)
phase 1: rapid repolarization (transient K exit)
phase 2: plateau (Ca entry and K exit)
phase 3: repolarization (K exit)
phase 4: resting membrane potential (Na/K pump and K leaking)

Question 2

what is excitation contraction coupling

Answer 2

process of AP arrival leading to myofibril contraction and relaxation

Question 3

myofibrils

Answer 3

actin and myosin

actin: thin filament
myosin: thick filament

Question 4

sarcomere

Answer 4

functional unit of contraction

Question 5

cross-bridge cycling

Answer 5

ATP dependent process of actin and myosin sliding to shorten the sarcomere

begins with Ca influx

Question 6

actin-troponin complex

Answer 6

tropomyosin fiber wraps around actin and covers the myosin head binding site on the actin –> prevents myosin binding

Ca must bind to troponin to cause tropomyosin to move off of myosin binding site

Question 7

troponin C

Answer 7

binding site for Ca on troponin complex

Question 8

troponin I

Answer 8

inhibits actin-myosin interaction by blocking the binding site

Question 9

troponin T

Answer 9

binds troponin complex to tropomyosin

Question 10

tropomyosin

Answer 10

supports actin and regulates interactions with myosin

Question 11

L type Ca channels

Answer 11

transports Ca from extracellular –> intracellular

opens in response to changes in membrane potential

Question 12

ryanodine receptors

Answer 12

transports Ca from sarcoplasmic reticulum to cytosol

opens in response to Ca influx from L type channels

Question 13

what is the main source of Ca used for contraction

Answer 13

sarcoplasmic reticulum

Question 14

SERCA

Answer 14

sarco-endoplasmic reticulum ATPase

transports Ca from cytosol back into the SR during recovery to allow for relaxation

Question 15

phospholamban

Answer 15

inhibits SERCA to slow down rate of relaxation –> ultimately slows HR and contractility

Question 16

PMCA

Answer 16

plasma membrane Ca ATPase

transports Ca from intra –> extracellular

Question 17

Na/Ca exchanger

Answer 17

transporters Ca from intra –> extracellular

Question 18

steps of contraction and relaxation of myocytes

Answer 18

1. cell depolarizes from opening of Na channels (phase 0)
2. extracellular Ca enters through L-type Ca channels (phase 2)
3. intracellular Ca triggers Ca release from SR via ryanodine receptors
4. increased cytosolic Ca –> binds troponin C –> pulls tropomyosin off of myosin binding site
5. actin-myosin cross bridging occurs to cause contraction
6. SERCA sequesters Ca back into SR
7. myocyte relaxes

Question 19

what two factors affect contractility

Answer 19

Ca concentration
Ca sensitivity

Question 20

what mediators and receptors are used in sympathetic stimulation of EC coupling

Answer 20

NE and epi
B1 adrenergic receptors

Question 21

effects of sympathetic stimulation on EC coupling

Answer 21

phosphorylation of:
1. L-type channels: phosphorylation increases Ca influx
2. Phospholamban: when phosphorylated, decreases SERCA inhibition –> increased rate of relaxation
3. troponin I –> increases rate of relaxation

NET: increased chronotropy, inotropy, dromotropy, and lusitropy

Question 22

what mediator is used in parasympathetic stimulation of EC coupling + effects

Answer 22

acetylcholine

NET: decreases chronotropy, inotropy, dromotropy, and lusitropy

Question 23

what is the cardiac cycle

Answer 23

sequence of mechanical and electrical events that occur during each heart beat

Question 24

what initiates the cardiac cycle

Answer 24

SA node

Question 25

systole

Answer 25

contraction and emptying AV valves: closed (prevent backflow) SL valves: open

Question 26

diastole

Answer 26

relaxation and filling AV valves: open SL valves: closed

Question 27

phase 1 of cardiac cycle

Answer 27

atrial contraction occurs at end of diastole to "top off" the ventricles AV: open SL: closed

Question 28

pressure during phase 1 of cardiac cycle

Answer 28

atrial = ventricular

Question 29

sounds heard during phase 1 of cardiac cycle

Answer 29

S4 sound normal in LA, abnormal in SA

Question 30

phase 2 of cardiac cycle

Answer 30

isovolumetric contraction occurs at start of systole to generate enough pressure to open SL valves AV: closed SL: closed

Question 31

pressure during phase 2 of cardiac cycle

Answer 31

end diastolic volume large increase in ventricular pressure small increase in atrial pressure

Question 32

sounds during phase 2 of cardiac cycle

Answer 32

S1 sound - closing of AV valves normal in all animals

Question 33

phase 3 of cardiac cycle

Answer 33

rapid ejection occurs during systole to push blood out of ventricles AV: closed SL: open

Question 34

pressure during phase 3 of cardiac cycle

Answer 34

ventricular = aortic pressure then ventricular pressure decreases as blood exits

Question 35

sounds during phase 3 of cardiac cycle

Answer 35

no sound any sounds heard = flow murmur

Question 36

phase 4 of cardiac cycle

Answer 36

reduced ejection occurs during end of systole to finish contraction via passive flow AV: closed SL: open

Question 37

pressure during phase 4 of cardiac cycle

Answer 37

aortic pressure slightly > ventricular pressure both are decreasing atrial pressure increases slightly as it continues to fill (venous return)

Question 38

sounds during phase 4 of cardiac cycle

Answer 38

none

Question 39

phase 5 of cardiac cycle

Answer 39

isovolumetric relaxation occurs during early diastole to begin active ventricular relaxation AV: closed SL: closed

Question 40

pressure during phase 5 of cardiac cycle

Answer 40

end-systolic volume ventricular < aortic pressure to cause SL valve closure increase in atrial pressure

Question 41

sounds during phase 5 of cardiac cycle

Answer 41

S2 sound - closure of SL valves normal in all species

Question 42

phase 6 of cardiac cycle

Answer 42

rapid/early filling occurs during diastole to allow for rapid ventricular filling/atrial emptying PASSIVE process - majority of filling AV: open SL: closed

Question 43

pressure during phase 6 of cardiac cycle

Answer 43

atrial pressure > ventricular pressure

Question 44

sounds during phase 6 of cardiac cycle

Answer 44

S3 sound normal in LA, abnormal in SA

Question 45

windkessel effect

Answer 45

aortic/arterial blood flow continues even during diastole aortic walls stretch during systole to store blood; walls contract during diastole to maintain organ perfusion

Question 46

phase 7 of cardiac cycle

Answer 46

reduced filling (diastasis) occurs during diastole; blood flow from atria to ventricles nearly stops AV: open SL: closed

Question 47

pressure during phase 7 of cardiac cycle

Answer 47

atrial pressure slightly > ventricular pressure mostly done filling at this point - rest occurs during phase 1

Question 48

sounds during phase 7 of cardiac cycle

Answer 48

none

Question 49

wiggers diagram

Answer 49

diagrams the change in atrial, ventricular, and aortic pressure during the cardiac cycle diagram is the same shape of the curve for R and L sides of the heart BUT right is at lower pressures

Question 50

how does right side stroke volume compare to left side stroke volume

Answer 50

equal - same amount of blood gets ejected

Question 51

how does right side pressure compare to left side pressure

Answer 51

right side < left side

Question 52

what does AV valve closure define

Answer 52

the start of systole

Question 53

what does SL valve closure define

Answer 53

the start of diastole

Question 54

what is stroke volume

Answer 54

the volume of blood ejected from the ventricle in one cardiac cycle SV = EDV - ESV EDV: end-diastolic volume (greatest ventricular volume) ESV: end-systolic volume (lowest ventricular volume)

Question 55

what is ejection fraction

Answer 55

the percentage of blood leaving the ventricle with each cycle EF = SV / EDV OR EF = (EDV - ESV) / EDV