USMLE Step 1 Respiratory Physiology Review 61 02 CO2 Transport

USMLE Step 1 Respiratory Physiology Review 61 02 CO2 Transport

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Play USMLE Audio MP3 61 02 CO2 Transport Below

Begin 61 02 CO2 Transport Transcription

Moving now to carbon dioxide transport. Carbon dioxide is the metabolic waste product formed in the tissues. From the tissues, it diffuses into systemic capillary blood and is then transported to the lungs for elimination from the body. Carbon dioxide is delivered to the lungs via the blood in three different forms.

List these three forms of CO2 alphabetically. I’ll cue you with the first letter of each.

First, B

  • bicarbonate

Second, C

  • carbaminohemoglobin

Third, D

  • dissolved CO2

What is carbaminohemoglobin?

  • Carbaminohemoglobin is carbon dioxide bound to hemoglobin.

What percent of the CO2 delivered to the lungs is in the form of bicarbonate ion?

  • About 65% of the carbon dioxide delivered to the lungs is bicarbonate ion.

What percent of the CO2 delivered to the lungs is in the form of carbaminohemoglobin?

  • About 25% is carbaminohemoglobin.

What percent of the CO2 delivered to the lungs is physically dissolved in the blood?

  • About 10% is dissolved CO2.

What is the following process called?

  • At the tissues carbon dioxide enters the blood and diffuses into the red blood cell where it is converted to bicarbonate. Bicarbonate ion then diffuses out of the red blood cell, into the plasma and is replaced by chloride.

Again, what is this process called? The two word answer starts with CS.

  • Chloride shift.

What happens to the chloride shift at the other end of the line when carbon dioxide is exchanged between the blood and the alveolar air?

  • In the lungs, the chloride shift is reversed.

Student doctor, please pause the tape and summarize what we’ve discussed about CO2 transport.

Carbon dioxide is the metabolic waste product formed in the tissues. From the tissues, it diffuses into the systemic capillary blood and is then transported to the lungs for elimination from the body. CO2 is delivered to the lungs via the blood in three forms. As bicarbonate ion, as carbaminohemoglobin, and as physically dissolved carbon dioxide. Carbaminohemoglobin is carbon dioxide bound to hemoglobin. About 65% of the CO2 delivered to the lungs is in the form of bicarbonate ion, about 25% as carbaminohemoglobin, and about 10% as physically dissolved CO2. At the tissues, carbon dioxide enters the blood and diffuses into the red blood cell where it is converted to bicarbonate. Bicarbonate ion then diffuses out of the red blood cell, into the plasma, and is replaced by chloride. This is called the chloride shift. At the other end of the line, in the lungs, the chloride shift is reversed.

 

 

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