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BRS - Cardio > Cardiac Mechanics > Flashcards

Cardiac Mechanics Flashcards

1
Q

What happens in a ventricular cell after an electrical event?

A

Calcium 2+ influx, calcium 2+ release, contractile event

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2
Q

What is a T-tubule?

A

finger-like invaginations from the cell surface in ventricular cells

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3
Q

Where are T-tubules located in relation to the myofibrils?

A

spaced so each T-tubule lies alongside each Z-line of every myofibril

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4
Q

What is the purpose of a T-tubule?

A

carries surface depolarisation deep into a cell

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5
Q

What percentage of ventricular cells are made up of myofibrils?

A

46%

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6
Q

What percentage of ventricular cells are made up of mitochondria?

A

36%

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7
Q

What percentage of ventricular cells are made up of sarcoplasmic reticulum?

A

4%

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8
Q

Where is the sarcoplasmic reticulum located in relation to T-tubules?

A

SR wraps around the T-tubule

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9
Q

What happens to a T-tubule in response to an action potential?

A

L-type calcium 2+ channels opens

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10
Q

What happens after L-type Ca 2+ channels open?

A

due to high conc gradient, ca 2+ moves into cell

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11
Q

What happens after the Ca 2+ influx into the cell?

A

some Ca binds to the myofilaments, majority binds to the RyR

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12
Q

What is a Ryanodine Receptor?

A

RyR, SR calcium-release channels

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13
Q

What happens after calcium binds to the RyRs?

A

calcium from stores inside the SR are released into cytosol so they can bind to myofilaments

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14
Q

What happens after the Ca 2+ binds to the myofilaments?

A

calcium is pumped against its conc gradient into the SR through Ca ATPase, ready for next action potential

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15
Q

What prevents Ca 2+ build up in the cytosol(?)?

A

during relaxation, some Ca is removed through Na/Ca exchange system using conc gradients

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16
Q

What is the relationship between intracellular Ca2+ and force production?

A

As Ca 2+ increases, there’s a sigmoidal relationship with force

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17
Q

What is the difference between cardiac muscle and skeletal muscle?

A

cardiac muscle = more resistant + less compliant than skeletal muscle

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18
Q

Why is cardiac muscle more resistant + less compliant than skeletal muscle?

A

due to properties of extracellular matrix + cytoskeleton

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19
Q

What happens to active force as muscle length increases?

A

active force has a bell curve relationship w/ muscle length - force reaches a peak at 100% muscle length

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20
Q

What happens to passive force as muscle length increases?

A

passive force increases gradually as muscle length increases - more so with cardiac muscle

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21
Q

What happens to total force as muscle length increases?

A

total force follows active force, with a higher peak due to increasing passive force

22
Q

What part of the force-muscle length relationship is important for cardiac muscle?

A

the ascending limb of the relation

23
Q

What two forms of contraction does the heart?

A

isometric + isotonic

24
Q

What is isometric contraction?

A

when muscle fibre lengths don’t change but pressure still increases in both ventricles

25
Q

What is isotonic contraction?

A

shortening of fibres + blood is ejected from ventricles

26
Q

What is preload?

A

the sarcomere stretch of cardiac myocytes at the end of ventricular filling during diastole

27
Q

What determines the preload on the ventricles before ejection?

A

ventricular filling / stretch

28
Q

What is preload dependent on?

A

venous return

29
Q

What are measures of preload?

A

End-diastolic volume, end-diatonic pressure + right atrial pressure

30
Q

What. is afterload?

A

the pressure the heart must work against to eject blood during systole (ventricular contraction)

31
Q

What is after load proportional to?

A

average arterial pressure

32
Q

What does an increase in after load result in?

A

decreases the amount of isotonic shortening that occurs + decreases the velocity of shortening

33
Q

What are measures of afterload?

A

diastolic blood pressure

34
Q

What does shorter muscle length mean (in terms of stretch)?

A

less stretch

35
Q

What does longer muscle length mean (in terms of stretch)?

A

more stretch

36
Q

What were the observations of Frank + Starling?

A

as filling of the heart increases, the force of contraction also increases

37
Q

What is the definition of the Frank + Starling relationship?

A

increased diastolic fibre length increases ventricular contraction

38
Q

What is the consequence of the Frank + Starling relationship?

A

ventricles pump greater stroke volume so that, at equilibrium, cardiac output balances the augmented venous return

39
Q

What are the 2 factors that cause the effect of stretch on the force of contraction?

A

changes in no. of myofilament cross bridges that interact + changes in calcium sensitivity of the myofilaments

40
Q

Why do changes in no. of myofilament cross bridges cause Frank-Sterling relationship?

A

at shorter lengths than optimal the actin filaments overlap on themselves –> reduces the no. of myosin cross bridges that can be made

41
Q

Why do changes in Ca2+ sensitivity of myofilaments cause a Frank-Sterling relationship?

A

• Ca2+ is required for myofilament activation
• Troponin C (TnC) is thin filament protein that binds Ca2+ and regulates formation of cross-bridges
between actin and myosin
• At longer sarcomere lengths the affinity of TnC for Ca2+ is increased due to conformational
change in protein
• Less Ca2+ required for same amount of force
• With stretch the spacing between myosin and actin filaments (lattice spacing) decreases so the probability of forming strong binding cross-bridges increases
• This produces more force for the same amount of activating calcium

42
Q

What is the definition of stroke work?

A

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

43
Q

What is the equation for stroke work?

A

stroke work = stroke volume (SV) x pressure (P)

44
Q

What is meant by stroke volume?

A

volume of blood ejected during each stroke

45
Q

What is meant by pressure?

A

pressure at which blood is ejected

46
Q

What influences stroke volume?

A

preload + afterload

47
Q

What influences pressure?

A

cardiac structure

48
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

49
Q

What is the equation for Law of LaPlace?

A

Wall Tension (T) = (Pressure (P) x Radius (R)) / Wall Thickness (h)

50
Q

What is the difference in radii of curvature between the 2 ventricles?

A

Radius of curvature of LV is LESS than the curvature of RV

51
Q

Why is there a difference in the radii of curvature of the 2 ventricles?

A

allows the left ventricle to generate higher pressures w/ similar wall stress

52
Q

What happens to failing hearts which increases wall stress?

A

they become dilated

BRS - Cardio (15 decks)

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