As I have understood it, only monomeric (monosaccharides) carbohydrates can pass from the intestine to the epithelial lining and on to the blood stream. But how is that possible without some sort of membrane protein like the kind H2O uses? Carbohydrates are generally very polar molecules. And why can monosaccharides do it, but not disaccharides and polysaccharides?
well there is a transport protein, and those transport proteins have specificity: they only transport a certain kind of molecule. for example, a transporter called the sodium-glucose symporter is responsible for the absorption of glucose. However, there can be paracellular transport – stuff can go between epithelial cells, so not everything is ultra-specific.