From the lumen of the small intestine to the small intestinal cell (called enterocyte), the barriers to diffusion is/are
|C||Unstirred water layer|
The luminal side of enterocyte is lined by brush border (made up of microvilli);
in turn, the microvilli is ‘covered’ by 2 layers (from lumen towards the cell) viz. :
- unstirred water layer
- glycocalyx layer (this is rich in neutral and amino sugars)
Thus, for a substance to enter the cell from the lumen, it has to cross the unstirred water layer, glycocalyx, brush border and the mucous layer.