USMLE Step 1 Respiratory Physiology Review 61 07 Diffusion 2_3

USMLE Step 1 Respiratory Physiology Review 61 07 Diffusion 2_3

On these “Gold Standard Step 1 Facts” pages you will find Free:

  • USMLE Audio Review files from our “Gold Standard USMLE Reviews”
  • Transcriptions of those files
  • And videos (as they become available)

The idea is that you can review for the USMLE online by:

  • Listening to the Audio
  • Following along with the transcription
  • Or by watching the video (if available)

If you like what you here, you can purchase the entire Gold Standard Step 1 MP3 audio USMLE review for your iPhone, iPod, or computer here.

Let’s start our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.

Play USMLE Audio MP3   61 07 Diffusion 2_3  Below

Begin   61 07 Diffusion 2_3  Transcription

What is the normal PO2 in the alveoli?

  • 100 mm Hg

What is the normal PO2 of blood entering the pulmonary capillaries?

  • About 40 mm Hg.

In addition to the steep pressure gradient what else aids in the transfer of oxygen between alveolar air and capillary blood?

  • The chemical reaction between oxygen and hemoglobin aids in the transfer of oxygen from alveoli to capillary blood.

Under normal conditions, how long does it take for the transfer of oxygen between the alveolar gas and capillary blood to be complete?

  • About .25 seconds

How long it take blood to pass through a pulmonary capillary?

  • About .75 seconds

A safety margin for gas exchange is provided by the fact that under normal circumstances, blood stays in the pulmonary capillary longer than is necessary for gas exchange to occur. How long is the safety margin?

  • About .5 seconds

During exercise or at high altitudes the safety margin allows adequate oxygen transfer to occur. How does high altitude affect oxygen tension of inspired air?

  • At higher altitudes, the oxygen tension of inspired air is lower than at sea level.

What affect does a lower alveolar PO2 have on oxygen diffusion rate in the lungs?

  • The diffusion rate decreases as alveolar PO2 decreases.

What is the normal carbon dioxide tension of blood entering the pulmonary capillaries?

  • 46 mm Hg

What is the normal PCO2 of alveolar air?

  • 40 mm Hg

Although the pressure gradient for carbon dioxide isn’t as great as for oxygen, what property of carbon dioxide helps it diffuse more rapidly than oxygen?

  • The high solubility of carbon dioxide in body fluids helps it diffuse more rapidly than oxygen

Student doctor, please pause the tape and summarize what has been discussed about gas transfer between blood in the pulmonary capillaries and alveolar air.

  • Normal PO2 in the alveoli is about 100 mm Hg. Normal PO2 of blood entering the pulmonary capillaries is about 40 mm Hg. Besides the steep pressure gradient, the chemical reaction between oxygen and hemoglobin also aids in the transfer of oxygen from alveoli to capillary blood. Under normal conditions, oxygen transfer is complete in about .25 seconds. It takes blood about .75 seconds to pass through a pulmonary capillary. A safety margin for gas exchange is provided by the fact that under normal circumstances, blood stays in the pulmonary capillary longer than is necessary for gas exchange to occur. The safety margin is about half a second long and for healthy lungs allows adequate oxygen transfer to occur during exercise or at high altitudes. At higher altitudes, the PO2 of inspired air is lower than at sea level which causes the diffusion rate of oxygen to decrease. The normal PCO2 of blood entering the pulmonary capillaries is about 46 mm Hg. And normal PCO2 of alveolar air is 40 mm Hg. The high solubility of carbon dioxide in body fluids helps it diffuse more rapidly than oxygen.

 

****END OF TRANSCRIPTION****

Want More USMLE Step 1 Review Facts?

boardprep.net

Leave a Reply