Why Are Pulmonary Alveoli and Kidney Nephrons Spherical Instead of Tetrahedral?

AI Thread Summary
The discussion centers on the structural similarities between pulmonary alveoli and kidney nephron capsules, both designed to maximize exposure for efficient gas exchange and filtration. The conversation highlights the importance of surface area-to-volume ratios, noting that while a tetrahedron would theoretically provide the best ratio, both structures are spherical, with alveoli having a ratio of 5.25-4.8. The question posed is why nature favors this spherical shape despite the potential advantages of a tetrahedral form. Key points include the role of surface tension in alveoli, where a spherical shape allows for even distribution of tension, crucial for their function during breathing. The adaptability of alveoli size during respiration is also mentioned as a factor that may benefit from a spherical design. Overall, the discussion emphasizes the balance of various biological factors influencing the shapes of these organelles.
edwardone123
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In a human body we have two relatively similar structures -pulmonary alveoli(https://www.google.com/url?sa=i&sou...aw1ZCQJEi4eFj0awKq5CtTeT&ust=1555210875346706)
and kidney nephrone capsule
(https://qph.fs.quoracdn.net/main-qimg-0633a201014408ed330c31420225e4e6.webp)

Both of these organelles has similar function- provide maximal exposure (max volume of processed air/blood ) for given volume.
In lungs we would expect,that alveoli would give max amount of air to blood surrounding alveoli ,in kidneys -that capusle of nephrone would expose max amount of primary urine to contact with blood behind some barriers.
In both cases it would be logical to think that we need shape of these organelles to have max surface to volume ratio .
According to (https://en.wikipedia.org/wiki/Surface-area-to-volume_ratio ) the ideal shape for this task would be tetrahedron(A/v ratio -7.21)
In reality we have sphere -capsule with ratios 5.25-4.8
Why Mother Nature would not change it shape ?
Do you see any benefits in spherical shape ?
Please do not mention turbulence as an argument for spherical/capsule shape
Thank you
 
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Often selection will drive biology to a compromise position to balance several different factors.
In the case of the alveoli, factors other than packing that may be involved:
Surface tension in the alveoli is strong enough in the small alveoli to be important and is regulated to maintain it properly. Spheres will equalize the tension over the surface of the alveoli, a shape with flat sides and angular edges would have an uneven distribution of tension over its surface. I expect that they would tend to equalize on the very small scale involved to forma sphere. I expect that this would be a major factor. Alveoli change size during breathing. This may work better with a spherical shape.
 
also interesting :
 
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