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Cardiovascular mechanics Flashcards

(29 cards)

1
Q

Explain what is needed in order for a single ventricular cell to contract

A

Action potential

Calcium ion influx and release

contractile event

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2
Q

Describe the parameters (length and width of a single ventricular cell)

A

100uM in length

15uM wide

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3
Q

Describe the structure of T tubules and how much do they open up due when theres an action potential? Where do that carry AP to?

A

Finger like invagination from cell surface

opens up to 200nm in diameter

it is spaced so that T tubule lies alongside each Z line of every myofibril

carries surface depolarisation deep into cell

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4
Q

Describe the 3D component of a single cardiac cell structure in terms of organelles distribution

describe significance of mitochondria

A

Myofibrils, mitochondria, nucleus, SR

mitochondria - 36%; need large ATP

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5
Q

Describe the excitation- contraction coupling in the heart?

A
  • Ca2+ moves into sarcoplasm via L-type calcium channel
  • stimulate ryanodine receptor in SR to release Ca ions
  • same amount of Ca2+ that entered now leave sarcoplasm via Na+/Ca2+ transporter to avoid bulid up of Ca2+.. this doesnt use ATP; only electrical gradient.
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6
Q

What’s the relationship w=etwwen intracellular Ca ions and force production

A

There’s a threshold needed but it’s SIGMOIDAL

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7
Q

What is the relationship between length and tension? what other factors increase

A

The longer the muscle the higher the maximum contractility force (iSOMETRIC contraction)

There’s also more PASSIVE FORCE

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8
Q

Contrast skeletal and cardiac muscle

what causes these differences

A
  • Cardiac muscle more resistant to stretch
  • LESS compliant than skeletal muscle

this is due to differences in properties of ECM and cytoskeleton

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9
Q

in the relationship between length and tension, What limb is only important/relavant for cardiac muscle

A

Ascending limb of graph; heart muscle doesnt pull as it is contained in pericardial sac unlike skeletal muscle

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10
Q

What are two forms of contraction that the heart uses ? which occurs earlier?

A
  • Isometric- muscle fibres doesnt change in length but pressure increases
  • Isotonic- shortening of fibres and blood is ejected

theres isometric FIRST then isotonic

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11
Q

What is the law of LaPlace

A

When pressure within a cylinder is led constant, the tension on it’s walls increases with increasing radius

wall tension = (P X R)/h

Pressure in vessel, R= radius of vessel

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12
Q

what is preload?

A

Blood fills the heart during diastoles and stertches resting ventricular walls.

this fills ventricles and the stretching determines the pre-load

allows heart to adapt its force to the volum of blood it recieves

Dependent on venous return

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13
Q

what are the measures of pre-load?

A
  • END-DIASTOLIC VOLUME
  • END-DIASTOLIC PRESSURE
  • RIGHT ATRIAL PRESSURE
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14
Q

what is after load?

what si the signifcance of increase in afterload?

A

THE PRESSURE in which the ventricles MUST WORK against to OPEN the aortic valve.

high afterload means there’s less amount of isotonic shortening. Also less velocity of shortening

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15
Q

what are the measures of afterload?

A

Diastolic blood pressure

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16
Q

what does an increase in pre load affect?

A

increase in ISOMETRIC CONTRACTION

17
Q

what does an increase in after load affect?

A
  • shorter ISOTONIC contraction
  • lower VELOCITY of contraction

note the change in gradient of velocity

18
Q

describe the Frank-Starling relationship?

A

Increased diastolic fibre length (due pre-load) will increase ventricular contraction.

hence ventricles pump greater stroke volume; at equilibrium, cardiac output exactly balances augemnted venous return

19
Q

what are the potential causes of the frank-starling relationship

A
  • Changes in number of myofilament crossbridges formed- the more stretched, the more cross bridges can form
  • Changes in Ca2+sensitivity of the myofilaments
20
Q

descirbe hypothesis 1 for increase in Ca senstivity

A

at longer sarcomere length, the affinity of troponin C for Ca2+ increases due to change in protein structure

21
Q

describe the other hypothesis for the starling relationship

A

With higher length, there’s decreasing myofilament lattice spacing, the probabilty of forming strong bidning cross-bridges increases

22
Q

what is stroke work?

give equations? what affects each value?

A

Stroke work= Stroke volume x Pressure at which blood is ejected

SV; affected by pre-load AND after load

Pressure- affetced by cardiac structure

hence stroke work is work done by heart to pump blood under pressure into aorta or pulmonary artery

23
Q

How does radius of curvature affect Tension using Law of Laplace?

A

Lower radius of curvature increases pressure as thickness is taken into consideration

hence HIGHER PRESSURE; Tension is the same

those with failing heart have heart with HIGHER radius of curvature; more work and pressure on heart

24
Q

Does skeletal muscle need influx of extracellular calcium in order to contract?

A

No; ONLY CARDIAC muscle cells do

25
Contrast the structure of T-tubules to SR, between skeletal muscle and caridac muscle, in terms of recptors and connections
Skeletal muscle; theres a DIRECT mechanical link between L-type receptor and ryanodine recptor on SR; hence depolarisation in L type receptor directly opens up ryanodine receptor CARDIAC- no connection; there's a space for Ca2+ to enter and activate ryanodine receptor
26
what is responsible for passive force?
Cytoskelton stretching, NOT MYOFILAMENT SLIDING
27
what is the correct answer?
B
28
what is the correct answer
C hardening of Pulmonary artery affect AFTERLOAD NOT PRELOAD
29
whar is the correct order for this?
F,C,A,H,E,B,G,D