The hexoses glucose, galactose and fructose serve as basic fuel molecules for eucaryotic cells. These molecules are unable to diffuse across cellular membranes, and require transporter proteins for entry into and exit from cells. Each of the transporters has different affinities for glucose and the other hexoses, which largely dictates their function. Hexose transporters also have fairly distinctive patterns of expression among tissues.
Most cells express more than one hexose transporters.
Consider for example, small intestinal epithelial cell, which must absorb glucose, galactose and fructose from the intestinal lumen, then export those sugars into blood. This cell has at least three hexose transporters. On the basolateral plasma membranes is GLUT2, which allows diffusion of all three of these hexoses out of the cell into extracellular fluid and ultimately, into blood. The hexose transporters are large integral membrane proteins. Also, they all appear to be glycosylated on one of the extracellular loops.