Sucrose is broken down at the Brush border by sucrase into fructose and glucose, while lactose is broken down by lactase into galactose and glucose. Also at the brush border. Now, the reason we have to break down the carbohydrates ultimately into their individual monumeric constituents is because the intricacies, the cells of the small intestine, can only absorb these monomers. That means it cannot absorb disaccharides because they're simply too big. So we have to break down the disaccharides into our individual monomers. Now, the question is, once we actually break down the disaccharides into glucose, galactose and fructose on the microvilli at the brush border of anterocytes, what exactly takes place then?