Glucose Carrier Proteins in Cell Membranes
First thing's first: there are many different kinds of glucose transporters (genes), even within the same organism. These genes share partial sequence identity in mammals, and are part of the SLC2A, or "GLUT" gene family. In yeast, there exist glucose- and galactose-specific transporters.

Often, not always, a glucose transporter type may be tissue specific. GLUT3 is expressed in neurons, in the placenta, and elsewhere. Compare this to the expression of GLUT1, found in red blood cells, and GLUT4, found in adipose and skeletal muscle tissue.

Each kind of transporter has various affinities for glucose (or other sugars for that matter), and various levels of permeability for similar molecules. This is what is called the specificity of the transporter. The rate at which sugars can pass through the pore of the transporter is called the frequency. Together, these properties define the function of a hexose transporter, and hence why there are different kinds with site-specific expression across the body.

In terms of regulation: GLUT1 is dynamically regulated based on available glucose (up-regulated during shortage and down-regulated during excess). This is not the case with GLUT4; instead, GLUT4 is insulin-regulated, so that muscles and fat tissues can uptake glucose for storage, which is a hormone-controlled process.

Here is a great webpage to help you understand the characteristics of hexose transporters, especially with regard to galactose, fructose and glucose.