Dialysis membrane is simply a passive permeability barrier through which molecules can pass if they are small enough. If the molecules form aggregates due to low solubility in the aqueous medium, they may not permeate well.

Rat intestine may contain bile acids, which act as detergents to keep low-solubility molecules in solution. The cells contain metabolic enzymes that can change the molecule chemically. There may also be active transporters in the epithelial cells lining the intestine that cause the molecules to be taken up onto the cells.

Thank you for your answer but sir if you use intestine for ex vivo studies then also smae thing will happen?

To the extent that the biological functions of the intestinal cells are maintained.

Thanx sir for giving the answer