Cardiac muscle Flashcards

1
Q

Describe the flow of ox and de ox blood through the major blood vessels of the heart

A
  • Dexoxygenated blood goes into the vena cava and leaves through the pulmonary artery to the lungs (pulmonary circuit)
  • Oxygenated blood from the lungs enters through the pulmonary vein and leaves through the aorta to the entire body (systemic )
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2
Q

What is cardiac muscle called?

A

Myocardium

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3
Q

Describe the structure of cardiac muscle

A
  • Striated - repeated sarcomeres
  • one or two central nuclei
  • adjacent cells connected though intercalated disks (desmosomes)
  • has troponin and tropomyosin like skeletal muscle
  • branched cells (myocytes)
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4
Q

What is the func of intercalated disks?

A
  1. provide strong anchorage
  2. for electrical communication
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5
Q

Why does the left side of heart have a thicker myocardium?

A
  • needs much more force than RHS as it is pumping blood around the body
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6
Q

Describe the term pacemaker potential

A
  • no steady RMP
  • instead it undergoes a slow depolarisation called a pacemaker potential
  • brings MP to threshold where AP’s are generated
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7
Q

What are nodal cells?

A
  • Cells that produce an electrical impulse through a pacemaker potential
  • eg the SA node in the right atrium of the heart
  • the hearts natural pacemaker cell - constantly produces AP’s
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8
Q

Describe the excitation - contraction coupling in the myocardium - generation of AP

A
  • Na+ entry into cell causes depolarisation
  • this depolarisation causes L type Ca2+ channels to open in T tubules
  • Trigger Ca2+ enters cytosol and binds to the ryanodine receptor on SR
  • Ca2+ then flows into cytosol
  • Ca2+ binds to troponin and cross bridge cycle begins - sliding flilament mech
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9
Q

What controls cardiac muscle ?

A
  • Spontaneous electrical activity
  • ANS - sympathetic increases heart rate and parasympathetic decreases heart rate
  • note hormonal secretions and stretch have effect to
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10
Q

What is phase 0 of ventricular AP?

A
  • when the AP reaches the myocyte & depolarization begins
  • fast Na+ voltage gated channels open but they inactivate rapidly
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11
Q

What is phase 1 of ventricular AP?

A
  • after Na+ channels become inactivated, there is a period of brief repolarization
  • K+ channels open and outward flow of K+
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12
Q

What is phase 2 of ventricular AP?

A
  • consists of a plateau period where Ca2+ enters the cell through L type (long opening) voltage gated Ca2+ channels
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13
Q

What is phase 3 of ventricular AP?

A
  • as the plateau progresses, K+ efflux increases due to the opening of voltage gated K+ channels
  • these channels are called slowed rectifier K+ channels
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14
Q

What is phase 4 of ventricular AP?

A
  • the resting membrane is re- established
  • 75-90% of the raised Ca2+ in the cytosol is pumped back to the sarcoplasmic reticulum via the Ca2+- ATPase
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