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Cvr > Cardiovascular Mechanics > Flashcards

Cardiovascular Mechanics Flashcards

1
Q

What ion produces a contractile event?

A

Calcium

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2
Q

What happen when you remove calcium from the extracellular space of cardiac tissue?

A

The cardiac tissue will not contract

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3
Q

What are T-Tubules?

A

Finger like invaginations from the cell surface that are spaced such that each T tubule lies alongside the Z line of every myofibril

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4
Q

What do T tubules do?

A

Allow the excitatory depolarisation event to travel deep into the cell

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5
Q

What is the lace like structure above the sarcomeres?

A

Sarcoplasmic reticulum

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6
Q

What is the function of the sarcoplasmic reticulum?

A

holds and stores calcium

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7
Q

What percentage of volume of cardiac cell does the sarcoplasmic reticulum occupy?

A

4%

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8
Q

What channels lie in the T tubule membrane?

A

L type calcium channels

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9
Q

What receptors lie above the L-type calcium channels

A

Ryanodine receptors

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10
Q

Where are ryanodine receptors found?

A

Embedded within the sarcoplasmic reticulum membrane

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11
Q

What are SR calcium release channels?

A

Ryanodine receptors

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12
Q

What structure is involved with detecting the action potential / depolarisation event?

A

The L type calcium channel

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13
Q

What first happens when a depolarisation event is detected?

A

Ca2+ ions from outside the cell enter through the calcium channels

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14
Q

What two things happen to the calcium which enter into the L-type Ca2+ channel?

A

Most binds to Ryanodine receptor but some goes to sarcomere for muscle contraction

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15
Q

What happen when the ryanodine receptor binds calcium?

A

Undergoes a conformation change, and allows stored calcium to be released from the sarcoplasmic reticulum into the cytoplasm

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16
Q

What happens to the stored calcium that is released from the sarcoplasmic reticulum?

A

Binds to the myofilaments to initiate muscle contraction

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17
Q

What is the calcium induced calcium release effect?

A

When calcium comes and binds to the ryanodine receptor, to trigger the release of more calcium from the sarcoplasmic reticulum

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18
Q

How is relaxation of the muscle brought about?

A

The calcium ions are taken back up into the sarcoplasmic reticulum by SR Ca2+ ATPase

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19
Q

What is the sodium calcium exchanger?

A

A protein embedded in the T tubule which allows calcium to leave into the extracellular space to trigger relaxation of the muscle

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20
Q

What is the balance between the amount of calcium entering into the cell, and leaving the cell?

A

They are equal

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21
Q

What does force production depend on?

A

The concentration of intracellular calcium

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22
Q

What is the relationship between force production and calcium concentration in the cytoplasm?

A

Sigmoidal relationship

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23
Q

What happens to the amount of force produced when you increase the stretch on the muscle?

A

The amount of force produced increases

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24
Q

What is passive force?

A

As you stretch a muscle fibre more, the elasticity this results in is called the passive force - like a recoil force

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25
Q

What happens to passive force as you stretch cardiac muscle more?

A

Passive force increases

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26
Q

What is meant by isometric contraction?

A

Contraction that produces forces without the muscle shortening

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27
Q

What is total force?

A

Active force + Passive force

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28
Q

Between cardiac and skeletal, which produces more passive force?

A

Cardiac muscle

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29
Q

Why does cardiac muscle have a larger passive force?

A

Cardiac muscle is more resistant to stretch, so when it does get stretched the passive elastic recoil force it can produce is greater

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30
Q

Why is cardiac muscle more resistant to stretch?

A

The properties of the extracellular matrix and cytoskeleton

31
Q

Why does cardiac muscle only work on the ascending limb?

A

Because you cannot over stretch cardiac muscle

32
Q

Why does the active force fall when you overstretch skeletal muscle?

A

Because stretching it too much decreases the interdigitation between actin and myosin, so active force falls away

33
Q

Why can cardiac muscle not be over stretched?

A

Physiological constraints - The heart is contained within the pericardium

34
Q

what are the two forms of contraction the heart uses?

A

Isometric contraction and Isotonic contraction

35
Q

What is isometric contraction?

A

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

36
Q

What is isotonic contraction?

A

Shortening of fibres resulting in the ejection of blood from the ventricles

37
Q

During isometric contraction, why is blood not ejected from the ventricle?

A

The valves are shut

38
Q

Why does the pressure increase in the ventricle during isometric contraction?

A

Because the cardiac muscle is contracting against. blood volume

39
Q

When does isotonic contraction take over?

A

When the pressure in the ventricle is greater than the pressure in the aorta

40
Q

What is the preload?

A

The amount of stretch the muscle experiences before it is actually stimulated to contract

41
Q

What is the afterload?

A

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

42
Q

When is the afterload encountered?

A

when the muscle has started to contract

43
Q

When is isometric contraction in play?

A

During ventricular filling

44
Q

What is the relationship between the shortening of muscle and the afterload?

A

As the afterload increases, the amount of shortening decreases

45
Q

For the same afterload what happens to the shortening of a longer muscle length?

A

More shortening

46
Q

What is the preload defendant on?

A

Venous return

47
Q

What is the after Load?

A

The load against which the left ventricle ejects blood after opening the aortic valve

48
Q

What is the after-load proportional to and why?

A

Arterial pressure - the arteries have smooth muscle and therefore can contract, increasing the pressure - this pressure can then back up towards the aorta as well

49
Q

What happens to velocity of contraction when you increase the afterload?

A

It decreases

50
Q

What happens to the amount of isotonic shortening when you increase the afterload?

A

It decreases

51
Q

What are measures of preload?

A

End diastolic volume, end diastolic pressure and right atrial pressure

52
Q

What are measures of the afterload?

A

Diastolic blood pressure

53
Q

Why is high blood pressure not a good thing for the heart?

A

Higher blood pressure means the heart has to work harder to efflux blood from the ventricles

54
Q

How does the force of contraction relate to venous return?

A

Venous return affects the preload, and a larger pre load increases the force of contraction

55
Q

What is the Frank-Starling law?

A

Increased diastolic fibre length increases ventricular contraction

56
Q

What is the consequence of the Frank-Starling Relationship?

A

A greater stroke volume is observed when the venous return and hence preload increases

57
Q

How does the heart have its own intrinsic regulatory mechanism?

A

Pumps out exactly the same amount of blood that returns to it

58
Q

What two factors cause Thr Starlings Law?

A

The change in the number of myofilaments cross bridges that interact

The changes in the Ca2+ sensitivity of the myofilaments

59
Q

Relationship between shorter lengths of muscle fiber and strength of contraction?

A

Shorter lengths that optical mean actin filaments overlap, which reduces the number of myosin cross bridges that can be made so less contracttion

60
Q

What happens to interdigitation when you stretch a muscle fibre?

A

It increases and more cross bridges are formed

61
Q

How does the stretch of muscle affect the Ca2+ sensitivity?

A

Longer sarcomere lengths increases the affinity of Troponin for Ca2+ due to a conformational change in the protein

62
Q

How is force affected by Ca2+ sensitivity?

A

The higher the Ca2+ sensitivity, The more cross bridges will form - this means more force is produced for the same amount of activating calcium

63
Q

What is the lattice spacing hypothesis?

A

With stretch, the space between the myosin and actin filaments decreases, so the probability of forming strong binding cross bridges increases, hence producing more force with the same amount of activating calcium

64
Q

What is the definition stroke work?

A

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

65
Q

How do you calculate stroke work?

A

Stroke work = the volume of blood ejected during each stroke x the pressure at which the blood is ejected

66
Q

What is the stoke volume greatly impacted by?

A

The preload and the afterload

67
Q

What affects the pressure at which the blood is ejected from the ventricle?

A

Cardiac structure

68
Q

What is the definition of the law of LaPlace?

A

When the pressure in a cylinder is held constant, the tension on its walls increases with an increase in radius

69
Q

What is the formula for wall tension?

A

(Pressure in vessel x radius of vessel) / wall thickness

70
Q

Which ventricle has a larger radius of curvature?

A

The Right ventricle

71
Q

Use the Law of LaPlace to explain why the pressure is higher in the Left Ventricle?

A

The tension in the walls of both ventricles is the same, and given that T = Pressure x Radius, since the radius of the left ventricle is lower, the pressure must to higher to compensate for this

72
Q

What happens to wall stress in failing hearts?

A

Wall stress increases due to dilation

73
Q

How does adrenaline secretion affect preload?

A

Ádrela one increases the venous return, and therefore increases the preload

74
Q

What factors affect the afterload?

A

Stenosis or hardening of the artery

Cvr (13 decks)

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