Cardiac Muscle 2 Flashcards

1
Q

How is force modulated?

A
  • increase rate of automaticity
  • increase dimensions f the ventricles (increased stretch) (starlings law)
  • use neurotransmitters to alter rate and Ca2+ handling
  • inotropic drugs
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2
Q

What is contraction force dependent of?

A

Intracellular calcium as well as total calcium (this includes reserves of buffered calcium in the SR)

TWO main ways: the amplitude and duration of the calcium transient; altered myofilament calcium sensitivity

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3
Q

What factors alter calcium sensitivity?

A

Sarcomere length- ^ means greater contraction
Acidosis- more acidic means decreased force
Catecholamines- increased decreases force
caffeine!

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4
Q

What pumps are activated when pH changes in myocytes?

A

More alkaline, acid loaders such as CHE and CBE

More acidic acid extruders, such as NBC and NHE

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5
Q

How would heart failure best be treated drugs that increaseor decrese calcium senstivity?

A

You would think increase however this shorten relaxation time. If they have diastolic heart failure, not good. No correct answer and is circumstantial

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6
Q

What is the frank starling concept?

A

An increase in end diastolic ventricular volume increases SV via a stretch induced increase in contractility

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7
Q

What is the biphasic response to stretch in the heart?

A

Rapid: to do with increased myofilament sensitivity due to strecth
If you prolong stretch, the increase in force is due to the increase in the calcium transient

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8
Q

What is the force frequency response?

A

That there is an increase in force of contraction with an increase in heart rate due to:-

  • increased intracellular sodium (due to more depolarization), meaning more sodium calcium exchange occuring meaning more intracellular calcium.
  • less time for calcium extrusion

this loads the SR, increased calcium transient

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9
Q

What is the one counter intuitve aspect of sympathetic activation on the heart

A

It increased calcium influx and thus transient, but will decrease TnC sensitivity for calcium, so as to allow relaxation

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10
Q

Describe Beta adrenergic stimulation of the heart

A

The heart has beta drenergic receptors, that control inotropic, lusitropic and chronotropic state of the heart.\

beta agonists stimulate adenyl cyclase, increasing cAMP, which will stimulate PKA which will phosphorylate: SL channels (^ Ica); phospholamban (increase SR uptake); SR release through RyR’s; TnI which inhibits TnC but the other stuff compensates

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11
Q

What are some drugs that modulate cardiac force?

A

Digoxin (cardiotonic steroids) which inhibit the Na/K ATPase, meaning increased intracellular sodium, meaning more NCX activity, increasing Ica. Serious side effects
Sympathomimetics: B1 agonists but will desensitive
Bipyridines which inhibit phosphodiesterase, increasing cAMP

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