USMLE Step 1 Physiology Review 56 09 Frank-Starling Curve (1_3)

USMLE Step 1 Physiology Review 56 09 Frank-Starling Curve (1_3)

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Play USMLE Audio MP3 56 09 Frank-Starling Curve (1_3) Below

Begin 56 09 Frank-Starling Curve (1_3) Transcription

Now lets talk about the Frank-Starling curve . According to the Frank-Starling effect, the energy by the heart  is a function of what?

  • The end diastolic

What is another term that means the initial length of muscle fibers?

  • Preload

In the intact heart what does preload depend on?

  • It depends on the volume of blood in the ventricle just before contraction

What is another way of stating the volume of blood in the ventricles just before contraction?

  • VEDV.

VEDV is proportional to and therefore interchangeable with VEDP and central venous pressure when discussing Frank-Starling related cardiac volume relationships. What effect does an increased VEDV or VEDP have on cardiac fibers?

  • It lengthens them

How does lengthening the cardiac fibers lead to stronger contractions? (You may want to pause the tape here)

  • Within optimal limits, lengthening the cardiac fibers create more possibilities for cross-bridging. Additional cross-bridges allow the heart to generate more force with each contraction. An increase in preload provides more contraction so the heart can pump more blood with each stroke.

Student doctor please pause the tape and summarize the information discussed this far on Frank-Starling mechanism.

  • According to the Frank-Starling effect, the energy by the heart is a function of the end diastolic length cardiac muscle fibers. Preload refers to the initial length of muscle fibers.In the intact heart, preload depends on the volume of blood in the ventricle just before contraction. Another way of stating the volume of blood in the ventricles just before contraction is VEDV. VEDV is proportional to and therefore interchangeable with VEDP and central venous pressure when discussing Frank-Starling related cardiac volume relationships. An increased VEDV or VEDP lengthens cardiac fibers. Within optimal limits, lengthening the cardiac fibers create more possibilities for cross-bridging. Additional cross-bridges allow the heart to generate more force with each contraction. An increase in preload produces a stronger contraction so the heart can pump more blood with each stroke.

Now for some more question on the Frank-Starling mechanism. The Frank-Starling mechanism performs a crucial balancing act. What balancing act am I talking about?

  • Balancing the output of the two sides of the heart.

In addition to preload contractility of the ventricles affect stroke volume. What is another term for increased contractility?

  • Positive Inotropism

Define Inotropic?

  • Relating to muscle contraction

At a given level of diastolic volume or preload, what does positive inotropism allow for?

  • Increased contractile force and therefore stroke volume.

The administration of this drug which is derived from a flowering plant can lead to positive inotropism, what is the drug?

  • Digitalis

How does the administration of digitalis increase the force of cardiac contraction?

  • By raising intracellular Calcium concentration

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

  • First question was about the balancing act that the Frank-Starling mechanism plays. The Frank-Starling mechanism balances the output of the two sides of the heart. In addition to preload contractility of the ventricles affect stroke volume. Increased contractility is Positive Inotropism. The word Inotropic means relating to muscle contraction. At a given level of diastolic volume or preload, positive inotropism allow for increased contractile force and therefore stroke volume. The administration of Digitalis which is derived from a flowering plant can lead to positive inotropism. The administration of digitalis increase the force of cardiac contraction by raising intracellular Calcium concentration.

Through what other mechanism other than the administration of Digitalis does positive inotropism occur?

  • Through the activation of the Beta 1 receptors

Where are beta 1 receptors located?

  • In the myocardium

What nervous system are Beta receptors part of?

  • The sympathetic nervous system

What are the two ways to activate the beta receptors?

  •  First, sympathetic nerve stimulation; second, the administration of drugs such as epinephrine or norepinephrine

Like the administration of Digitalis, activation of beta 1 receptors increases the concentration of Calcium within the cell which results in a more forceful contraction. What part of the endocrine system does the nervous system stimulate to release the Norepinephrine and epinephrine?

  • The adrenal medulla

What percentage of the epinephrine and norepinephrine is released from the adrenal medulla is epinephrine?

  • 85% of the total release

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

  • The first question was about the activation of beta 1 receptors. In addition to the administration of Digitalis, activation of the Beta 1 receptors can also lead positive inotropism occur. Beta 1 receptors are located in the myocardium and are part of the sympathetic nervous system. Sympathetic nerve stimulation and the administration of drugs such as epinephrine or norepinephrine activate beta 1 receptors. Like the administration of Digitalis, activation of beta 1 receptors increases the concentration of Calcium within the cell which results in a more forceful contraction. The sympathetic nervous system stimulates the adrenal medulla to release the Epinephrine and Norepinephrine. 85% of the total release from the adrenal medulla is epinephrine.

Okay back to some more questions on the Frank-Starling mechanism. What receptors are affected by the epinephrine?

  • Beta 1

What three drugs directly act on the Beta 1 receptors?

  • Epinephrine, Isoprotenol, Dobutamine

Which is stronger Epinephrine or Isoprotenol?

  • Isoprotenol

What drug works via the CNS to cause Epinephrine release that acts on the beta 1receptors?

  • Dopamine

Look at the graph that shows the three different ventricular function curves. The graph with the VEDV on the x axis , and the stroke volume on the y axis, As inotropy increases, what happens on the slope of the curve that describes  relationship between stroke volume and VEDV?

  • It gets steeper, therefore for a small relative increase in the VEDV, there is a greater relative increase in stroke volume

What state will the body be in for positive inotropism to occur?

  • The state of exercise or the fight or flight response.

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

  • The first question was about which receptors are affected by Epinephrine. Beta 1 receptors are affected by the epinephrine. Epinephrine, Isoprotenol, and Dobutamine directly act on the Beta 1 receptors. Isoprotenol is stronger Epinephrine. Dopamine works via the CNS to cause Epinephrine release that acts on the beta 1receptors. As inotropy increases, the slope of the curve that describes the relationship between stroke volume and VEDV gets steeper, therefore for a small relative increase in the VEDV, there is a greater relative increase in stroke volume. The body will be in a state of exercise or fight or flight response for positive inotropism to occur.

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