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The Respiratory Surface and Gas Exchange Efficiency

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  • 0:05 Gas Exchange: The…
  • 1:20 Gas Exchange Is Efficient
  • 1:48 Gas Exchange Is Fast
  • 2:34 High Surface Area
  • 3:12 Gases Are Lipid-Soluble
  • 3:44 Lesson Summary
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Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

The respiratory membrane includes millions of alveoli with a surface area as large as a tennis court. This large respiratory surface area, combined with other factors, makes for efficient gas exchange to meet our metabolic needs.

Gas Exchange: The Respiratory Surface

Oxygen and carbon dioxide move across the respiratory membrane
Respiratory Membrane Diagram

You may appreciate the fact that we breathe to get air into and out of our lungs. Have you ever wondered what happens inside the lungs? As we look closely, we can see that gas exchange occurs in the lungs between the air and our blood. Now, gas exchange in the lungs refers to the movement of oxygen into the blood and carbon dioxide out of the blood. Oxygen and carbon dioxide move across what we call the respiratory surface, and that consists of an alveolar epithelial cell and a pulmonary capillary endothelial cell. Now, this respiratory surface is also referred to as the respiratory membrane. Note that the air is on one side of the membrane and blood is on the other side of the membrane. As you can see from the image above, oxygen moves out of the alveolar air into the blood, while carbon dioxide moves in the opposite direction. Therefore, we use the term gas exchange, as oxygen is exchanged for carbon dioxide across the respiratory surface.

Gas Exchange Is Efficient

Our bodies require a lot of oxygen to help our cells make the energy they need to do work. Likewise, we need to get rid of the carbon dioxide that's made by our cells when they work. Therefore, gas exchange needs to be efficient to get enough oxygen into our body - and ultimately to our cells - and to get the carbon dioxide out of the body. So, let's discuss some of the factors that help gas exchange.

Gas Exchange Is Fast

First of all, gas exchange is extremely fast. The respiratory membrane is very thin, as it consists of only two cells - that is, the alveolar epithelial cell and the pulmonary capillary cell. The distance for gas exchange is only about a half a micrometer. That's smaller than the width of even your thinnest hair! This short distance allows gas exchange to occur very quickly. Furthermore, gases move across the respiratory membrane by diffusion, which is the movement of a substance from a high to a low concentration. Diffusion is extremely fast for short distances. If you put a drop of food coloring in a glass of water, for example, you can see just how fast diffusion occurs.

High Surface Area

The large amount of alveoli on the lung surface makes gas exchange efficient
Lung Surface Diffusion

Additionally, gas exchange is efficient because of the large surface area available for gas exchange. Each of our lungs contains hundreds of millions of these tiny alveoli. Gas exchange occurs across each of the alveoli. This large number of alveoli greatly increases the surface area for gas exchange. Now, the total surface area of alveoli is about 140 square meters or 1,500 square feet. Wow! That's about the size of a tennis court. So, if you wonder why we have alveoli, well, now you know.

Gases Are Lipid Soluble

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