USMLE Step 1 Physiology Review 56 10 Frank-Starling Curve (2_3)

USMLE Step 1 Physiology Review 56 10 Frank-Starling Curve (2_3)

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Play USMLE Audio MP3 56 10 Frank-Starling Curve (2_3) Below

Begin 56 10 Frank-Starling Curve (2_3) Transcription

The middle curve represents normal ventricular function or straight Frank-Starling mechanism relation. What does the bottom curve represent?

  • Negative inotropism

What is another term for negative inotropism?

  • Decreased contractility

How does filling time relate to increased inotropy?

  • More filling time leads to a greater preload which leads to greater stretch and contractility.

What drug causes greater contractility via two methods, by inhibition of the Sodium/Potassium ATPase and by aiding Calcium influx during phase two of the action potential?

  • Digoxin

What class of drug does Digoxin belong to?

  • Cardiac glycosides

What is the reason intrinsic to the heart for decreased inotropy?

Loss of myocardial tissue

Student doctor please pause the tape and summarize the information discussed since the last summary on Frank-Starling mechanism.

  • First question was about negative inotropism. The middle curve represents normal ventricular function or straight Frank-Starling mechanism relation. The bottom curve represents negative inotropism. Decreased contractility is another term for negative inotropism. More filling time leads to a greater preload which leads to greater stretch and contractility. Digoxin causes greater contractility via two methods, by inhibition of the Sodium/Potassium ATPase and by aiding Calcium influx during phase two of the action potential. Digoxin belong to the class of drugs known as Cardiac glycosides. A reason intrinsic to the heart for decreased inotropy is loss of myocardial tissue.

What two physiological factors of the heart can lead to less preload?

  • Weak atrial contraction and less filling time

What autonomic interaction decreases inotropy?

  • Direct parasympathetic inhibition

Direct parasympathetic inhibition takes place via what kinds of receptors?

  • Muscarinic

In what part of the heart does direct parasympathetic inhibition take place?

  • In the atria only

How does the parasympathetic inhibition of the atrial contraction lead to decreased inotropy?

  • less preload

What is the main class of drugs that decreases inotropy?

  • Beta blockers

What is the main example of a Beta blocker?

  • Propanolol

What two receptors do beta blockers block?

  • Beta 1 and beta 2

Student doctor please pause the tape and summarize the information discussed since the last summary of the Frank-Starling mechanism

  • The first question was about what physiologic factor can lead to less preload. Weak atrial contraction and less filling time can lead to less preload. Direct parasympathetic inhibition decreases inotropy and takes place via Muscarinic receptors. Direct parasympathetic inhibition takes place in the atria only. The parasympathetic inhibition of the atrial contraction leads to decreased inotropy because there is less preload. Beta blockers is the main class of drugs that decreases inotropy. Propranolol is the main example of a Beta blocker. Beta blockers block beta 1 and beta 2 receptors.

****END OF TRANSCRIPTION****

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