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CV physiology (from notes) > Cardiac Muscle > Flashcards

Cardiac Muscle Flashcards

1
Q

Sliding filament mechanism

A

Actin filaments slide along w adjacent myosin filaments with cycling of CROSS-BRIDGES
Z lines come closer together
Cardiac muscle produces force/tension
Actin and myosin move away from each other - passive

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2
Q

2 principles of cardiac muscle

A
  • cardiac muscle requires no nervous input

- if you stretch it more than normal there will be a stronger force of contraction

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3
Q

What underlies the ability of the heart to control stroke volume

A

Its ability to increase its contractile force with a slight increase in its length
if the muscle is overstretched, active tension decreases

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4
Q

What is preload

A

Stretched condition of the heart muscle at the end of diastole

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5
Q

What does an increased preload result in

A

Increased EDV, increased SV

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6
Q

Greater force of contraction =>

A

Greater stroke vol

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7
Q

Is blood left in the heart at the end of systole

A

YES so it doesn’t seize

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8
Q

What does every point on the starling curve have

A

THE SAME CONTRACTILITY (NOT the same as force of contraction)

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9
Q

What is contractility

A

SV for a given EDV - inherent ability of the heart to contract

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10
Q

Effect of sympathetic activity on starling curve

A

A higher starling curve => increased contractility
THEREFORE
a higher SV for the same EDV

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11
Q

What happens to ventricular pressure during the ISOVOLUMETRIC PHASE of systole
=> what is a good measure of contractility

A

VP rises (think - VP must rise above AP to open valve)
Max rate at which VP rises = dP/dt max - this is a GOOD MEASURE OF CONTRACTILITY
therefore
anything causing slope to rise increases contractility

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12
Q

What sort of agent causes an increase in contractility

A

+ve inotropic agent

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13
Q

What sort of agent causes a decrease in contractility

A

-ve inotropic agent

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14
Q

What is a powerful inotropic agent

A

Ca2+

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15
Q

What are positive inotropic agents

A 
Noradrenaline
Adrenaline
increased Ca2+ influx and uptake by SR
Increased EC Ca2+
SLOPE IS ALMOST VERTICAL
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16
Q

What are negative inotropic agents

A 
hypoxia
drugs
Ca2+ channel blockers
beta adrenergic blockers 
SLOPE IS ALMOST HORIZONTAL
17
Q

What does Digoxin do

A

Increases IC Ca2+

Blocks Na+/K+ pump, slowing Na+-Ca2+ exchange

18
Q

Where is the RYR density high

A

High near L-type Ca2+ channels

19
Q

What facilitates CICR

A

Short distance between Ca2+ channels and RYR

20
Q

What stops the release of Ca2+ from the SR

A

Inactivation of RYR by increased [Ca2+]

Local depletion of SR calcium

21
Q

3 mechanisms for decreasing IC [Ca2+]

A
  1. SERCA
  2. Na+/Ca2+ exchange pump
  3. Cell membrane ATP-dependent Ca2+ pump
22
Q

SERCA (70% in humans)

A

Regulated by phospholamban which inhibits Ca2+ uptake // SR

therefore Ca2+ pumps Ca2+ from cytoplasm into SR stores

23
Q

Na+/Ca2+ exchange pump (most of remainder)

What is it powered by

A

Powered by Na+ GRADIENT

24
Q

Cell membrane ATP-dependent Ca2+ pump

A

Small amount

25
Q

What does sympathetic stimulation of cardiac muscle produce

A

Increase in active tension
Increase in rate of T development
Increase in rate of T relaxation

26
Q

Starling’s Law of the heart

A
  • increased filling of ventricles
  • increased SV
  • increased muscle fibre length
  • increased force of contraction
27
Q

Muscle basis for starling’s law of the heart

A

Increased stretching of muscle fibre increases sensitivity of Troponin C for Ca2+ => a stronger force of contraction

28
Q

Relaxation of heart

  • cAMP
  • PKA
A

cAMP activates PKA
PKA phosphorylates L-type Ca2+ channel
Increase in IC Ca2+ conc increases the force of contraction
PKA phosphorylates Phospholamban and Troponin I

29
Q

What does the phosphorylation of troponin I by PKA do

A

Inhibition of binding of Ca2+ to troponin C => relaxation/lusitropic effect

30
Q

What does the phosphorylation of PLN by PKA do

A

Decreases inhibition of SERCA
=> increased uptake of Ca2+ into SR
=> RELAXATION
SR are loaded with more Ca2+ for next contraction

31
Q

What does PLN phosphorylation promote

A

Rate of contraction

CV physiology (from notes) (10 decks)

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