Glucose is a water soluble molecule and in previous questions you have looked at the fact that water soluble molecules do not passed directly through the cell membrane because of its lipid core. How can we enable glucose absorption from the gut, glucose entry into the cells and glucose reabsorption in the kidneys?

Ions and molecules that can't pass directly through the cell membrane can pass through using channels or carriers. The channels are like tunnels through the cell membrane through which ions can pass down their concentration gradient. The channels can be open all the time or gated. Gated channels will only allow ions to pass when the channels are open. Carriers can physically move ions and molecules through the cell membrane. If the movement is down the concentration gradient, and the carriers are simply helping the process, this is known as facilitated diffusion. If the movement is against the concentration gradient and the carriers are actively pumping the molecules this is known as active transport.

We use carriers to move glucose through cell membranes. One group of carriers is known as the GLUTs (glucose transporter). They move glucose through the cell membrane the process of facilitated diffusion. In other words glucose is always moving from an area of higher concentration to lower concentration, and no energy is required for this to occur. The other main group of transporters are the SGLTs (sodium glucose transporter) which transport sodium and glucose simultaneously. Transporters which carry more than one ion or molecule at the same time are known as symports.