Things that change contractility Flashcards

1
Q

Summarise the effect of sympathetic stimulation on contraction (4)

A
  • more and faster Ca2+ release
  • faster cross bridge cycling
  • more and faster contraction
  • faster relaxation
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2
Q

Factors affecting heart rate are called what?

A

Chronotropic factors

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3
Q

Factors affecting contractility are called what?

A

inotropic factors

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4
Q

Factors affecting contraction and relaxation are called what?

A

lusitropic factors

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5
Q

As well as affecting heart rate via the cells in the SA node, how does sympathetic stimulation affect contraction via the muscle cells?

A

When NE binds to the β1-adrenoreceptor on the cardiac muscle cells, there is a rise in cAMP which activates PKA

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6
Q

What is the effect of there being a rise in cAMP in the cardiac muscle cells when noradrenaline binds to the β1-adrenoreceptor on contractility and contraction duration?

A

PKA phosphorylates

  • voltage gated L-type Ca2+ channels which increases Ca2+ concentration
  • RyR which increases the SR Ca2+ release
  • TnI which limits the interaction of Ca2+ with TnC which DECREASES Ca2+ sensitivity
  • PLB which releases the SERCA inhibition to increase SR Ca2+ uptake
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7
Q

How does sympathetic stimulation affect the Frank-Sterling mechanism and the pressure volume loop?

A

It shifts the Frank-Starling curve up because there is a higher SV for the same EDV
On the pressure volume loop, it means there is an increase in contractility which means that the SV increases, the ESV decreases

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8
Q

Due to an increase in heart rate by noradrenaline/norepinephrine, the duration of the twitch has to __________

A

shorten

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9
Q

Why is it important that noradrenaline leads to a decrease in Ca2+ sensitivity of the myofilaments?

A

to allow the heart to contract more quickly and relax more quickly to maintain appropriate ventricular filling during diastole

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10
Q

What 5 things come in response to sympathetic stimulation?

A
  • increased heart rate
  • elevated contractility
  • reduction in duration of diastole and systole
  • increase in conduction velocity
  • better synchronisation of atrial and ventricular contractions
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11
Q

Which hormones lead to an increase in CONTRACTILITY (not contraction duration)? How do they do this?

A
Short term:
- catecholamines such as adrenaline and dopamine which act the same way as the sympathetic stimulation
- glycosides such as digoxins/digitalis
Long term:
- Angiotensin II
- endothelin
- thyroid hormone
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12
Q

Ηοw do glycosides affect contractility?

A

They inhibit the Na+/K+ pump and so there is an accumulation of Na+. This inhibits the Ca2+ efflux through the Na+/Ca2+ exchanger

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13
Q

What are three hormones that decrease contractility?

A

Acetylcholine
Calcium blockers
β blockers

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14
Q

What receptor does acetylcholine bind to cause a decrease in contraction?

A

M2 muscarinic receptors

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15
Q

What is the effect of acetylcholine binding to the cardiac cells leading to a decrease in contractility?

A
  • there is a decrease in cAMP which means that there is less PKA activity which means that there is:
  • no activation of L-type Ca2+ channels which leads to a decrease in Ca2+ entering the cell
  • no activation of the RyR which decreases the Ca2+ release from the SR
  • there is INCREASED Ca2+ sensitivity because TnI does not limit the interaction with TnC
  • activates PLB which increases SERCA inhibition to decrease in SR Ca2+ uptake
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16
Q

What is the effect of beta-blockers leading to a decrease in contractility?

A

β-blockers block the β adrenoreceptor which reduces the cAMP levels and reduces the PKA activity. This leads to a eduction in the activity of the voltage gated T-type calcium channels, RyR and SERCA. It also increases the Ca2+ sensitivity of TnC and reduces the need for ATP so there is less stress on the heart