USMLE Step 1 Respiratory Physiology Review 60 17 Oxygen Dissociation Curve

USMLE Step 1 Respiratory Physiology Review 60 17 Oxygen Dissociation Curve

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Begin 60 17 Oxygen Dissociation Curve Transcription

Now let’s talk about the oxygen dissociation curve. A picture of the oxygen dissociation curve is included in your outline. Although partial pressure is a measure of the oxygen dissolved in the plasma, it is a clue to the amount of oxygen in the hemoglobin.

The normal oxygen dissociation curve is for what type of blood?

  • Oxygenated arterial blood.

The curve is a plot of the PO2 of oxygenated arterial blood versus what other quantity?

  • Hemoglobin saturation with oxygen

Increases in what three things will cause the oxygen dissociation curve to shift to the right. I’ll cue you with the first letter of each. By the way, one of the cues will be a number rather than a letter.

First, P

  • Partial pressure of carbon dioxide or you could say carbon dioxide tension

Second, T

  •  temperature.     

Third, 2

  • 2-3DPG.

A decrease in what factor will also cause the curve to shift to the right?

  • Decreased pH also causes the curve to shift right.

Student doctor, pause the tape briefly and just list the four changes that will cause the oxygen dissociation curve to shift to the right.

  • Increased partial pressure of carbon dioxide, increased temperature, increased 2-3 DPG, and decreased pH.

What effect do these factors have on hemoglobin?

  • They decrease the affinity of hemoglobin for oxygen.     

And what process does this facilitate?

  • Decreased oxygen affinity facilitates the delivery of oxygen to the tissues during periods of high demand.

What process commonly causes this shift by increasing partial pressure of carbon dioxide, decreasing pH, and increasing temperature?

  • Exercise of muscles in the periphery.

How does an increase in 2,3 DPG shift the curve to the right?

  • When 2,3 DPG binds to the beta chains of hemoglobin, hemoglobin’s affinity for oxygen is decreased.

Adaptation to what condition causes an increase in 2,3 DPG? The two word answer starts with CH.

  • Chronic hypoxemia.

And what is the common cause of chronic hypoxemia?

  • Chronic hypoxemia is commonly caused by living at high altitude.

Student doctor please pause the tape and summarize what has been discussed about the oxygen dissociation curve and the things that will cause it to shift to the right.

  • Although partial pressure is a measure of the oxygen dissolved in the plasma, it is a clue to how much oxygen is in the hemoglobin. The normal oxygen dissociation curve is for oxygenated arterial blood. The curve is a plot of the PO2 of oxygenated arterial blood versus hemoglobin saturation with oxygen. Increases in partial pressure of carbon dioxide, PCO2, temperature, and 2,3 Diphosphoglycerate, or 2,3 DPG will cause the oxygen dissociation curve to shift to the right. Decreased pH also causes the curve to shift right. These four factors decrease the affinity of hemoglobin for oxygen, which facilitates the delivery of oxygen to the tissues during periods of high demand. The affinity of hemoglobin for oxygen is the ease with which hemoglobin combines with oxygen. This right shift is commonly caused by exercise of muscle in the periphery because this increases PCO2, decreases pH and increases temperature. An increase in 2,3 DPG will shift the curve to the right because hemoglobin’s affinity for oxygen is decreased when 2,3 DPG binds to the beta chains of hemoglobin. Adaptation to chronic hypoxemia causes an increase in 2,3 DPG. Chronic hypoxemia is commonly caused by living in high altitude.

 

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