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Cardiovascular and Haematology (PHAR1017 ) year 1 > heart physiology > Flashcards

heart physiology Flashcards

1
Q

what is the membrane potential of a cell (Vm)?

A

potential difference between inside and outside of the cell

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2
Q

what is an action potential?

A

when tissues excite and cell are stimulated causing a change in potential causing nerve impulse or contraction of muscle

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3
Q

draw diagram of membrane potentials?

A

slide 3
lecture 8 heart physiology

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4
Q

what is depolarization?

A

cell becomes more positve

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5
Q

what is repolarization?

A

returns to negative resting potential

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6
Q

what is hyperpolarization?

A

more negative than resting potential

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7
Q

what are intercalated discs?

A

fibres joined end-to-end by specialized functions

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8
Q

what are properties of intercalated discs?

A

tight interactions
mediate electrical coupling
fibres branch to increase interconnections
one central nucleus
a lot of mitochondria

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9
Q

why are conrtactions synchronized?

A

to make sure cardiomyocytes work together and that the cardiac muscle works as syncytium

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10
Q

how are gap junctions formed?

A

by connexin

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11
Q

what is connexin?

A

integral membrane proteins

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12
Q

what is the purpose of a gap junction?

A

link cytoplasm to ensure rapid transfer of ions

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13
Q

how does the SA node cause contraction of the heart muscle?

A

intrinsic waves of excitation spread from SA to node to AV node from right atrium to left atrium via Buchmann’s bundle then to myocytes via bundle of His and purkinje fibres

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14
Q

what is the SA node controlled by?

A

autonomic system signals

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15
Q

what does the heart muscle consist of?

A

myocardial and cardiomyocyte fibres

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16
Q

what are the differences between SAN and myocardium?

A

electrical membrane potentials are different in SAN and myocardium

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17
Q

what happens to pacemaker cells?

A

If channels open causing depolarization by slow movement of K+ out of cell and faster movement of Na+ into cell occurring and close as threshold potential reached. Some Ca2+ channels open when threshold reached then lots of Ca2+ channels open causing overshoot. Ca2+ channels close and K+ channels open causing repolarization as K+ moves out of the cell and hyperpolarization occurs. K+ channels close and increase in electrical potential causing If channels to open again

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18
Q

draw diagram of action potential of cardiomyocytes?

A

slide 12
lecture 8 heart physiology

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19
Q

what are the phases in action potential in cardiomyocytes?

A

Phase 4:resting phase
outward leak of K+ through inward rectifier channels Na2+ and Ca2+ channels are closed
Phase 0:Depolarization
action potential triggered causing rise in TMP
Na+ channels open and Na+ enters the cell
threshold reached and rapid depolarization occurs causing overshoot
Na+ channels close and some Ca2+ channels open
Phase 1: early repolarization
TMP slightly positive
Some K+ channels open and K+ leaves cell causing TMP to reach 0 again
Phase 2:Plateau phase
small influx of Ca2+
important in the excitation-contraction coupling process
K+ movement out and down its concentration gradient via delayed rectifier K+ channels
TMP maintained at plateau as its electrically balanced
Phase 3:repolarization
L-type Ca2+ channels close
more K+ ions flow out than Ca2+ flowing in
TMP reaches resting potential

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20
Q

when is normal transmembrane ionic concentration gradient reached?

A

when Na+ and Ca2+ are returned to extracellular environment and K+ to the interior

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21
Q

what are the pumps involved in contractile system?

A

sarcolemmal Na+-Ca2+ exchanger
Ca2+-ATPase
Na+-K+-ATPase

22
Q

what is the refractory period of cardiomyocytes?

A

longer than other muscle cells
they have physiological mechanisms that allow for ventricles to empty and refill before next contraction

23
Q

what are thin filaments composed of?

A

actin

24
Q

what are thin filaments composed of?

A

myosin

25
Q

what is the sarcomere?

A

unit of muscle that contracts

26
Q

diagram to show sarcomere in cardiomyocytes with labels?

A

slide 18
lecture 8 heart physiology

27
Q

what are myosin?

A

thin filaments that include myosin ATPase and globular heads

28
Q

what is actin?

A

thick filaments
two strands arranged in an a-helix form

29
Q

what is tropomyosin?

A

double helix structure between actin filaments to prevent contraction

30
Q

what is troponin?

A

along actin strands

31
Q

what are the three troponins?

A

Troponin T
Troponin I
Troponin C

32
Q

what is the role of Troponin T?

A

ties troponin to actin

33
Q

what is the role of Troponin I?

A

inhibits ATPase

34
Q

what is the role of Troponin C?

A

binds calcium ions

35
Q

what is Calcium-induced calcium release used for?

A

excitation contraction coupling

36
Q

what happens when Ca2+ influx isn’t enough to trigger an action potential?

A

CICR amplifies signal triggering greater release of Ca2+

37
Q

what do invaginations (T-tubules do)?

A

L-type Ca2+ brought into contact with ryanodine receptors
Ca2+ release receptors in sarcoplasmic reticulum

38
Q

what happens after Ca2+ enters the cell?

A

ryanodine receptors change conformation and cause a larger release of Ca2+`

39
Q

diagram and labelling of sarcoplasmic reticulum and Ca2+ signalling?

A

slide 21
lecture 8 heart physiology

40
Q

what is initiation?

A

action potential that occurs via pacemaker

41
Q

what is excitation contraction coupling?

A

starts with CICR:
action potential spreads across sarcolemma
T-tubules depolarized so voltage gated L-type Ca2+ channels open releasing Ca2+ opening ryanodine receptors causing calcium to bind to troponin C

42
Q

what is the contractile cycle?

A

Ca2+ binds to TnC inhibiting TnI
change in tropomyosin exposing active site
myosin head binds to actin active site and rows along actin using ATP
ADP released
another ATP binds to myosin head to release actin

43
Q

what happens during ATP-dependent reaction?

A

ATP hydrolysed allowing crossbridge formation
myosin head fired allowing it to pull itself along actin called a power stroke

44
Q

how is Ca2+ returned back to the sarcoplasmic reticulum?

A

ATPase causing Ca2+ to dissociate from TnC and tropomyosin inhibits the active site of actin

45
Q

what is the nervous system divided into?

A

sympathetic and parasympathetic

46
Q

what does the sympathetic nervous system consist of?

A

stress, excitement, exercise
norepinephrine

47
Q

what does the parasympathetic system consist of?

A

involves autonomic stimulation of heart
acetylcholine

48
Q

how does altering the sympathetic activity of pacemaker cells increase rate of potential?

A

norepinephrine increased
If channels activity increases
norepinephrine binds to B1adrenergic receptors activating cAMP
Increases If channel open time

49
Q

what is chronotropic?

A

increase in heart rate

50
Q

equation to calculate cardiac output?

A

heart rate * stroke volume

51
Q

how is stroke volume calculted?

A

end diastolic volume (EDV) - end systolic volume (ESV)

52
Q
A

Cardiovascular and Haematology (PHAR1017 ) year 1 (14 decks)

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