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Cardiovascular and Respiratory medicine > Cardiovascular Mechanics > Flashcards

Cardiovascular Mechanics Flashcards

1
Q

What does a ventricular cell require for contraction?

A

Calcium and excitation of the cell

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2
Q

Outline the basic process leafing up to the contraction of a ventricular cell

A

Electrical event (AP)
Calcium transient (amount of Ca 2+ in sarcoplasm increased for short period of time)
Contractile event

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3
Q

Can the hearts contractility be sustained by saline solution with bicarbonate of soda and potassium chloride?

A

No
Addition of lime or calcium salt will resort good contractility

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4
Q

Does skeletal muscle need external calcium for contraction?

A

No

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5
Q

What component of a ventricular cell takes up the largest voume?

A

Myofibrils (46%)

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6
Q

What are T-tubules?

A

Finger-like invaginations of the cell surface

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7
Q

Outline the dimensions of a ventricular cell?

A

Ventricular cell length is 100 micrometers and width is 15 micrometers

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8
Q

Outline the dimensions of T tubule

A

T tubule is 200nm in diameter
T tubules are separated by 2 micrometers, intermediate between each z line of myofibril transmitting surface depolarisation deep into the cell

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9
Q

First step of excitation contraction coupling

A

Depolarisation excites the L-type Ca 2+ ion channel, and opens it up

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10
Q

Second step of excitation-contraction coupling

A

Extracellular Ca 2+ diffuses into the cell

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11
Q

Step 3 of Excitation contraction coupling

A

Minor proportion of Ca 2+ activates actin filaments causing contraction

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12
Q

Step 4 of Excitation contraction coupling

A

Ca 2+ binds to Ryanodine receptor on SR.
Receptor undegoes conformational change (Ligand dated) opening RyR

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13
Q

Step 5 of excitation contraction coupling

A

Ca 2+ binds to TnC on actin filaments to stimulate shortening of sarcomere

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14
Q

Step 6 of excitation-contraction coupling

A

Ca 2+ actively pumped into stored position by Ca 2+ ATPase channels of SR
Same amount of Ca 2+ that entered the cell during depolarisation effluxed by Na-Ca exchanger

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15
Q

Graph showing relationship between force production and intracellular signalling

A

Sigmoidal curve
Intracellular cytoplasmic Ca 2+ subsequently results in greater force exerted by muscle

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16
Q

Explain the length-tension relation in cardiac muscle

A

As we increase length the active force produced also increases provided we stimulate the cardiac muscle

17
Q

What are active and passive force?

A

Active- dependant on sarcomere shortening (forces act in direction of points muscular attachment towards to the centre)
Passive- based on the resistance to the stretch of the muscle

18
Q

What is total force?

A

Addition of passive and active force

19
Q

Which type of muscle is more resistant to stretch and less compliant and why?

A

Cardiac muscle as it is surrounded by the pericardium so it is not able to stretch further- properties of its extracellular matrix and cytoskeleton

20
Q

Which limb (ascending or descending ) for cardiac muscle is important for the LTR?

A

only ascending

21
Q

What is isometric contraction

A

Isometric contraction is the generation of force from a muscle without the shortening of the muscle fibres or sarcomeres
Pressure increases in both ventricles

22
Q

What is Isotonic contraction

A

Shortening of fibres to generate force
Blood is ejected from ventricles

23
Q

Define preload

A

Degree to which cardiac muscle cells are stretched from the filling of ventricles prior to contraction

24
Q

Define afterload

A

The force that the ventricle must develop to pump blood effectively against the resistance in the vascular system.

25
Q

What does an increased preload do to contractility

A

Increased preload-> increased stretching -> increased force therefore increased contractility

26
Q

What is preload dependant on?

A

Venous return

27
Q

What do measures in preload involve?

A

End Diastolic pressure
End Diastolic volume
Right Atrial Pressure

28
Q

What effect does increased afterload have on isotonic contraction

A

Increased afterload leads to decreased amount of isotonic shortening and decreases velocity of shortening

29
Q

What do measures in afterload involve>

A

Diastolic blood pressure

30
Q

Define the Frank-Starling Relationship

A

Increased diastolic fibre length increases the ventricular contraction

31
Q

What is the consequence of the Frank-Starling Relationship

A

-Ventricles pump greater stroke volume so that, at equilibrium, cardiac output exactly balances augmented venous return

32
Q

What are the 2 factors that cause the Frank-Starling Relationship

A

Changes in the number of myofilament cross-bridges that interact.
Changes in Calcium sensitivity of the myofilaments

33
Q

How does the number of cross bridges affect the Frank-Starling relationship

A

Ventricular stretching increases contact between myosin heads with myosin binding sites presented by the thin actin filaments-lattice spacing decreases
Decreasing myofilament lattice spacing, increasing probability of forming strong binding cross-bridges provides more force for the same amount of activating calcium/

34
Q

How do changes in calcium sensitivity affect the Frank Starling relationship

A

Ca 2+ needed for myofilament activation.
Troponin C (TnC) binds Ca2+, moving tropomyosin off the myosin binding sites on actin.
At longer sarcomere lengths, affinity for TnC for Ca 2+ is increased because of conformational change in protein; less Ca 2+ required for equivalent amount of force

35
Q

What is stroke work?

A

Work done by heart to eject blood under pressure into aorta and pulmonary artery.
Stroke work = Stroke volume x presure

36
Q

What 3 factors affect stroke work?

A

Preload
Afterload
Contractility

37
Q

Define the Law of Laplace

A

When pressure within a cylinder is held constant, tension on its wall increases with increasing radius.
Wall tension = Pressure in vessel x Radius of Vessel incorporating thickness divide PxR by thickness

38
Q

Which ventricle of the heart generates greater pressure and why?

A

Radius of curvature of walls of left ventricle less than that of right so it can generate higher pressure with similar stress

Lower R therefore greater P as T is constant

39
Q

What happens to the structure of a failing heart/

A

Becomes dilated and spherical- increases wall stress.

Cardiovascular and Respiratory medicine (2 decks)

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