LN05
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I would like to know whether Alveoli having elastic walls is one of its adaptations. There are some websites that say this, but some do not mention. Thanks
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BobbJo
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(Original post by LN05)
I would like to know whether Alveoli having elastic walls is one of its adaptations. There are some websites that say this, but some do not mention. Thanks
I don't think so

I would rather talk about features that clearly increase efficiency of gas exchange (diffusion)


large surface area
one cell thick wall
moist

Alveoli are folded to increase their surface area to volume ratio, so more volume of air can diffuse in from the blood and and in from the bronchioles. The lining of the alveoli walls are also moist so the gases can easily dissolve. The walls are thin so the diffusion distance is short. They have a rich blood supply as the blood capillaries are close and have thin walls, so there is a steep concentration gradient. The concentration gradient steepness is increased more as the blood is highly concentrated with carbon dioxide while the alveoli have a high concentration of oxygen, favouring diffusion of carbon dioxide into the alveoli and oxygen into the capillaries.
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LN05
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(Original post by BobbJo)
I don't think so

I would rather talk about features that clearly increase efficiency of gas exchange (diffusion)


large surface area
one cell thick wall
moist

Alveoli are folded to increase their surface area to volume ratio, so more volume of air can diffuse in from the blood and and in from the bronchioles. The lining of the alveoli walls are also moist so the gases can easily dissolve. The walls are thin so the diffusion distance is short. They have a rich blood supply as the blood capillaries are close and have thin walls, so there is a steep concentration gradient. The concentration gradient steepness is increased more as the blood is highly concentrated with carbon dioxide while the alveoli have a high concentration of oxygen, favouring diffusion of carbon dioxide into the alveoli and oxygen into the capillaries.
Wow thanks. I probably have lost a mark in my test then, but I have spoken about all of the 3 things you mentioned in your post. Thanks a lot
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Jpw1097
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(Original post by LN05)
I would like to know whether Alveoli having elastic walls is one of its adaptations. There are some websites that say this, but some do not mention. Thanks
I suggest you read up about Fick's law - this will help when you answer any question about factors determining the rate of diffusion across a membrane.

Fick's law states that the rate of diffusion is proportional to the surface area, the concentration gradient (i.e. the difference in concentration on either side of the membrane) and inversely proportional to the thickness of the exchange surface - this means that if you increase the surface area and the concentration gradient, the rate of diffusion will increase, and if you increase the thickness of the exchange surfacce, the rate of diffusion will decrease.

In the lungs, there is a huge surface area - there are millions of alveoli which increases the rate of diffusion. There is also a steep concentration gradient across the alveoli; the concentration (or more technically, partial pressure) of oxygen is HIGH in the alveoli, but LOW in the pulmonary capillaries; the concentration/partial pressure of carbon dioxide in the alveoli is LOW, but HIGH in the pulmonary capillaries - this maximises the rate of diffusion across the blood-air barrier. This steep concentration gradient is maintained by the rich blood supply in the lungs - this ensures oxygen rich blood is cleared away to allow more oxygen to diffuse into the blood, and also ensures that more carbon dioxide rich blood is brought in to diffuse into the capillaries.

The exchange surface in the lungs is very thin. Alveoli are lined by simple (one layer), squamous (flatted) epithelial cells. The blood vessels in the lungs are lined by a single layer of flattened epithelial/endothelial cells - again, this is known as simple squamous epithelium. The epithelial cells and endothelial share a fused basement membrane (connective tissue which supports cells). Therefore, gases only have to diffuse through three layers - a thin, single layer of epithelial cells in the alveoli, the shared basement membrane, and the thin, single layer of endothelial cells in the blood vessels.

These are the main three factors that maximise the rate of diffusion across the blood-air barrier.
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LN05
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(Original post by Jpw1097)
I suggest you read up about Fick's law - this will help when you answer any question about factors determining the rate of diffusion across a membrane.

Fick's law states that the rate of diffusion is proportional to the surface area, the concentration gradient (i.e. the difference in concentration on either side of the membrane) and inversely proportional to the thickness of the exchange surface - this means that if you increase the surface area and the concentration gradient, the rate of diffusion will increase, and if you increase the thickness of the exchange surfacce, the rate of diffusion will decrease.

In the lungs, there is a huge surface area - there are millions of alveoli which increases the rate of diffusion. There is also a steep concentration gradient across the alveoli; the concentration (or more technically, partial pressure) of oxygen is HIGH in the alveoli, but LOW in the pulmonary capillaries; the concentration/partial pressure of carbon dioxide in the alveoli is LOW, but HIGH in the pulmonary capillaries - this maximises the rate of diffusion across the blood-air barrier. This steep concentration gradient is maintained by the rich blood supply in the lungs - this ensures oxygen rich blood is cleared away to allow more oxygen to diffuse into the blood, and also ensures that more carbon dioxide rich blood is brought in to diffuse into the capillaries.

The exchange surface in the lungs is very thin. Alveoli are lined by simple (one layer), squamous (flatted) epithelial cells. The blood vessels in the lungs are lined by a single layer of flattened epithelial/endothelial cells - again, this is known as simple squamous epithelium. The epithelial cells and endothelial share a fused basement membrane (connective tissue which supports cells). Therefore, gases only have to diffuse through three layers - a thin, single layer of epithelial cells in the alveoli, the shared basement membrane, and the thin, single layer of endothelial cells in the blood vessels.

These are the main three factors that maximise the rate of diffusion across the blood-air barrier.
Wow that is a lot!! Im only in year 8!

But thank you for your effort
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mpaprika
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good blood supply
thin walls
moist walls
large surface area
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LN05
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(Original post by mpaprika)
good blood supply
thin walls
moist walls
large surface area
Ok thanks
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