Absorption of oxygen: lungs' vs. other capillaries

[Loren Booda]

Is the surface area of the alveolar capillaries comparable to that of all other arterial capillaries?

 

[Moonbear]

Your thread title and question in your post are not really the same thing. Can you clarify what exactly you're interested in learning so we can answer appropriately?

 

[Loren Booda]

Moonbear,

Thank you.

I am asking whether the oxygen absorptive surface area of the circulatory system excluding the lungs is equivalent to that at them. I. e., does the efficiency for oxygen breathed in the alveoli equal that across all cell walls? I find it interesting that the smaller surface area of the lungs absorbs just as much oxygen inefficiently from the air as all cells inhale through osmosis.

 

[Dale]

I am not 100% sure on this, but iirc the total surface area of the alveolar capilaries is smaller than that of the total surface area of the systemic capillaries. However, the diffusion distance is much less, so that the pulmonary blood is fully oxygenated long before it transits the entire capillary.

 

[Loren Booda]

Wow! That may be what I am looking for.

 

[Dale]

Well, my Biomedical Engineering Principles textbooks lists the alveolar surface area as 70 m², and the diffusion distance as 0.1-1.0 um. The partial pressure of O2 in venous blood is listed as 40 mmHg and the partial pressure of O2 in alveolar air is listed as 104 mmHg. The partial pressure of O2 in arterial blood is listed as 95 mmHg with tissue interstitial fluid at 40 mmHg being in equilibrium with venous blood, but I cannot find the mean diffusion distance or surface area for systemic exchange.

 

[Loren Booda]

That's a more detail than I knew even existed. I once read in the 1964 (ha!) World Book that the total length of capillaries in the human body would wrap several times around the earth.

By "mean diffusion distance or surface area for systemic exchange," do you mean at the cellular level?

 

[Dale]

That's a more detail than I knew even existed. I once read in the 1964 (ha!) World Book that the total length of capillaries in the human body would wrap several times around the earth.

The same textbook gives the typical length of a capillary in dogs as 1 mm and the number as 1.2E9. So a dog's capillaries wouldn't wrap aroud the earth, but a human is bigger than a dog.

By "mean diffusion distance or surface area for systemic exchange," do you mean at the cellular level?

Yes, on the tissue side instead of the lung side.