Epithelial cells in the small intestine absorb lipids through simple diffusion but how does diffusion of lipids occur in the first place if they are insoluble in water? I thought that substances need to be dissolved in order to have concentration and therefore a concentration gradient?

  • $\begingroup$ Insolubility means they don't dissolve in water and may self-associate. That doesn't mean they cannot exist in aqueous environments. I'm not sure this question is clear enough to answer accurately. $\endgroup$ – James Feb 10 '18 at 16:47
  • $\begingroup$ Do you actually have a reference that supports your understanding as being correct? $\endgroup$ – Graham Chiu Feb 10 '18 at 17:23
  • $\begingroup$ vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/… "The major products of lipid digestion - fatty acids and 2-monoglycerides - enter the enterocyte by simple diffusion across the plasma membrane. A considerable fraction of the fatty acids also enter the enterocyte via a specific fatty acid transporter protein in the membrane." Essentially I would like to know if a non-soluble substance could diffuse in water because my current understanding is that only dissolved substances can. $\endgroup$ – ed116898 Feb 11 '18 at 0:01

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