[scientizscht (OP)]

Hello

With Fick's Law you get a result of moles per cm2 per second.

That cm2 unit of area is a geometrical/macroscopic or microscopic surface area?

The human intestine has a macroscopic length of 7m and perimeter 10-15cm. This means that it is about 1m2.

However due to the microscopic wrinkles its surface is 250m2.

Which area would you consider in Fick's Law? And what if the microscopic wrinkles are in the magnitude of nanometers?

Thanks!

[scientizscht (OP)]

Any idea?

[Bored chemist]

This is an interestingly practical example of a known problem in maths.
https://en.wikipedia.org/wiki/Coastline_paradox

The simple answer is that the area you use is the one measured in "steps" about the size of the molecules which are diffusing.