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Personal BRS cardiovascular and respiratory medicine > cardiovascular mechanics > Flashcards

cardiovascular mechanics Flashcards

1
Q

what happens when a ventricular cell receives an electrical event?

A

Ca2+ influx, Ca2+ release

then contraction

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2
Q

what is the coupling of the electrical event and the contractile event?

A

excitation-contraction coupling

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3
Q

what does the contraction of cardiac muscle depend on?

A

influx of calcium from outside the cell to the inside

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4
Q

what is the difference between cardiac muscle and skeletal muscle when placed in saline solution?

A

skeletal muscle would still contract

cardiac muscle needs calcium in the solution so will not contract

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5
Q

what is the size of a ventricular cell?

A

150um long and 15um wide

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6
Q

what are T-tubules?

A

finger-like invaginations of the ventricular cell surface

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7
Q

how large are T-tubules?

A

200nm in diameter

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8
Q

how much space between each T-tubule? and why?

A

2um apart
so each T-tubule lies alongside each Z-line of every myofibril
allows surface depolarisation to be carried deep into the cell

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9
Q

what is the sarcoplasmic reticulum for?

A

calcium store for the muscle cells

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10
Q

where is the sarcoplasmic reticulum found?

A

above the myofilaments

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11
Q

order the organelles in terms of their volume in cells of the heart

A 
myofibrils(46%)
mitochondria(36%)
sarcoplasmic reticulum(4%)
nucleus(2%)
others(12%)
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12
Q

what happens at the end of sarcoplasmic reticulum?

A

wrap around the T-tubules

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13
Q

what is LTCC?

A

L-type calcium channels

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14
Q

what are LTCCs closely linked to?

A

a cluster of ryanodine receptors (SR calcium release channel)

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15
Q

what senses the depolarisation from calcium influx?

A

L-type calcium channel it opens up allowing calcium to diffuse into the cytosol

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16
Q

what are the roles of the calcium that enter the cytosol?

A

to bind to SR calcium release channels

can feed to the myofilaments

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17
Q

what happens when calcium binds to the SR calcium release channel?

A

it opens up allowing calcium to leave from the sarcoplasmic reticulum and enter the cytosol

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18
Q

what happens to the calcium leaving the sarcoplasmic reticulum?

A

binds to troponin on the myofilaments and activates contraction

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19
Q

how is relaxation brought about?

A

calcium pumped against its concentration gradient via SR calcium ATPase using ATP (recycle calcium)

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20
Q

how does calcium efflux and why?

A

same amount of calcium that enters must leave
uses sodium/calcium exchange system
sodium moves in providing energy to expel calcium from the cell

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21
Q

what is the relationship between cytoplasmic calcium concentration and force?

A

increase in calcium increases force produced

sigmoidal(S shaped graph)

22
Q

what is the relationship between muscle length and force produced?

A

increase in length increases force produced
active force drops after a certain muscle length
passive force constantly increases with muscle length

23
Q

why is cardiac muscle more resistant to stretch and less compliant than skeletal muscle?

A

due to properties of the ECM and cytoskeleton

24
Q

what is the difference between cardiac muscle and skeletal muscle in terms of over stretching?

A

cannot over stretch cardiac muscle (only works on ascending limb of muscle length)

25
Q

what are the types of muscle contraction in cardiac muscle?

A

isometric

isotonic

26
Q

what is isometric contraction?

A

muscle fibres do not change length but pressure increases in both ventricles

27
Q

what is isotonic contraction?

A

shortening of fibres and blood is ejected from ventricles

28
Q

what is the preload?

A

weight that stretches muscle before it contracts

29
Q

what is the afterload?

A

weight not apparent to muscle in resting state; only encountered when muscle has started to contract

30
Q

what happens to force as preload increases?

A

it increases

31
Q

what happens to muscle shortening as after load increases?

A

amount of shortening is reduced and velocity

32
Q

what happens to muscle shortening as preload increases?

A

it increases shortening and velocity

33
Q

in cardiac muscle what is the preload?

A

ventricle filling with blood

34
Q

what is the afterload in cardiac muscle?

A

pressure in the aorta

35
Q

what is preload dependant upon?

A

venous return

36
Q

what are measures of preload?

A

end-diastolic pressure and volume aswell as right atrial pressure

37
Q

what happens to the amount isotonic shortening with increased afterload?

A

it decreases

38
Q

what is a measure of afterload?

A

diastolic blood pressure

39
Q

what is starlings law (frank-starling relationship)

A

as filling of heart increases the force of contraction is also increased
increased diastolic fibre length increases ventricular contraction

40
Q

what are the consequences of starlings law?

A

ventricles pump greater stroke volume so that, at equilibrium cardiac output exactly balances the augmented venous return
(balance between amount of blood pumped and the amount that enters the heart)

41
Q

why is the Frank-Starling relationship?

A

changes in the number of myofilament cross bridges that interact
changes to the calcium sensitivity of the myofilaments

42
Q

what happens to troponin C (TnC) with longer sarcomere length? (hypothesis 1)

A

affinity for calcium is increased because of a conformational change
less calcium required for same force

43
Q

what happens when we stretch muscle cells? (hypothesis 2)

A

we increase their length but decrease the space between actin and myosin filaments (increases probability of cross bridges
lattice spacing

44
Q

what is stroke work?

A

work done by heart to eject blood under pressure into the aorta and pulmonary artery

45
Q

what is the equation for stroke work?

A

volume of blood ejected during each stroke(SV) X pressure at which the blood is ejected(P)

46
Q

what is the law of LaPlace?

A

when the pressure within a cylinder is held constant, the tension on its walls increases with increasing radius

47
Q

what is the equation of wall tension?

A 
wall tension (T)= pressure in vessel(P) X radius of vessel( R) 
when incorporating wall thickness divide by h
48
Q

what is the comparison of pressure in either side of the heart?

A

right side is lower in pressure than the left

49
Q

how is tension maintained with different pressures?

A

change in radius of ventricles

less radius in left ventricles

50
Q

what often happens to failing hearts (radius)?

A

they become dilated and spherical

Personal BRS cardiovascular and respiratory medicine (3 decks)

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