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

In summary, spherical capsules are better than alveoli because they have more surface area to volume ratio.
  • #1
edwardone123
4
1
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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  • #2
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.
 
  • #3
also interesting :
 
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FAQ: Why Are Pulmonary Alveoli and Kidney Nephrons Spherical Instead of Tetrahedral?

1. What is surface area to volume ratio?

Surface area to volume ratio is a measurement that compares the surface area of an object to its volume. It is calculated by dividing the surface area by the volume.

2. Why is surface area to volume ratio important in science?

Surface area to volume ratio is important in science because it affects how efficiently substances can be exchanged between an object and its environment. This ratio is also used to understand the physical properties and behaviors of different materials.

3. How does surface area to volume ratio impact the diffusion of substances?

The surface area to volume ratio impacts the diffusion of substances because it determines the rate at which molecules can move in and out of an object. Objects with a larger surface area to volume ratio have a higher rate of diffusion compared to objects with a smaller ratio.

4. How does changing the size of an object affect its surface area to volume ratio?

Changing the size of an object directly affects its surface area to volume ratio. As the size of an object increases, its surface area increases at a slower rate than its volume. This results in a decrease in the surface area to volume ratio. Conversely, as the size of an object decreases, its surface area decreases at a faster rate than its volume, resulting in an increase in the surface area to volume ratio.

5. What are some real-world applications of surface area to volume ratio?

Surface area to volume ratio is used in various fields, such as biology, chemistry, and engineering. In biology, it is used to understand the efficiency of nutrient and gas exchange in cells. In chemistry, it is used to determine the reactivity of substances. In engineering, it is used to design structures with optimal strength and heat transfer capabilities.

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