USMLE Step 1 Physiology Review 56 13 Arterial Pressure Control

USMLE Step 1 Physiology Review 56 13 Arterial Pressure Control

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Play USMLE Audio MP3 56 13 Arterial Pressure Control Below

Begin 56 13 Arterial Pressure Control Transcription

Okay now for some questions on arterial pressure control. What three overall systems are working to control the mean arterial pressure? List them alphabetically (please pause the tape)

  • First= parasympathetic, Second =Renin-Angiotensin system, Third= Sympathetic

Which two systems are working primarily to raise mean arterial pressure?

  • Sympathetic and Renin-Angiotensin. 

How does the renin-angiotensin system raise mean arterial pressure?

  • By raising blood volume

What does increased blood volume lead to?

  • Increased venous return

What does the increased venous return lead to?

  • Greater preload therefore greater contractility therefore greater stroke volume

How does the sympathetic system raise mean arterial pressure?

  • By increasing peripheral vascular resistance

Via what receptor?

  • The alpha receptor

Student doctor please pause the tape and summarize the information discussed this far on Arterial pressure control.

  • The first question was what overall systems control the mean arterial pressure. The parasympathetic, renin-angiotensin system, and the sympathetic systems control mean arterial pressure. The Sympathetic and Renin-Angiotensin are primary ones raising mean arterial pressure. The renin-angiotensin system raises mean arterial pressure by raising blood volume. Increased blood volume leads to Increased venous return. Increased venous return lead to greater preload therefore greater contractility therefore greater stroke volume. The sympathetic system raises mean arterial pressure by increasing peripheral vascular resistance via what receptor the alpha receptor.

Now for some more questions on arterial pressure control. How does the sympathetic nervous system work indirectly to raise mean arterial pressure?

  • By raising contractility and venous tone.

What are the receptors?

  • Beta 1 for contractility and alpha for venous tone

What is the two step processes by which raising venous tone increases mean arterial pressure?

  • Increased venous tone means greater venous return and greater filling pressure that means greater preload which leads to greater contractility and greater stroke volume

The sympathetic stimulation of contractility and the venous tone lead to what?

  • Increased stroke volume

And increased stroke volume combined with what causes increased cardiac output?

  • Heart rate

Does the sympathetic nervous system have an effect on heart rate?

  • Yes

Via what receptor?

  • Beta 1

Student doctor please pause the tape and summarize the information discussed since the last summary on arterial pressure control.

  • The first question was about how the sympathetic nervous system works to raise mean arterial receptor. The sympathetic nervous system work indirectly to raise mean arterial pressure by raising contractility and venous tone via the beta 1 for contractility and alpha for venous tone. Increased venous tone means greater venous return and greater filling pressure that means greater preload which leads to greater contractility and greater stroke volume. The sympathetic stimulation of contractility and the venous tone lead to increased stroke volume. Increased stroke volume combined with increased heart rate lead to increased cardiac output. The sympathetic nervous system has an effect on heart rate via beta 1 receptors.

Okay now back to some more questions. What system can lower mean arterial pressure by lowering heart rate?

  • The parasympathetic system

Via what receptor?

  • Muscarinic number 2

What part of the CNS is controlling both the sympathetic and parasympathetic output?

  • The vasomotor center

And what is that responding to?

  • The baroreceptors

What is the renin-angiotensin system responding to?

  • Lowered renal blood flow pressure

In addition to raising blood volume what else does the renin-angiotensin system do to raise mean arterial pressure?

  • The renin-angiotensin system raises peripheral vascular resistance

Via what hormone?

  • Angiotensin 2

What is the hormone produced that raises blood volume?

  • Aldosterone

Student doctor please pause the tape and summarize the information discussed since the last summary on arterial pressure control.

  • The first question was about how the parasympathetic system can lower mean arterial pressure by lower heart rate. The parasympathetic system can lower mean arterial pressure by lowering heart rate Muscarinic number 2 receptors. The vasomotor center of the CNS is controlling both the sympathetic and parasympathetic outputs. Vasomotor center responds to baroreceptors. The renin-angiotensin system is responding to lowered renal blood flow pressure. In addition to raising blood volume via aldosterone, the renin-angiotensin system raises peripheral vascular resistance via Angiotensin 2 which raises mean arterial pressure.

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