How do the mechanisms for actively transporting glucose and sodium across an epithelium differ?

Question

Question is only suitable for medical students and health science graduates.

I understand the mechanisms of how the glucose and sodium work, but not sure about the differences. They both use a type of active transport on one side of the epithelial cell (primary or secondary for sodium, only secondary for glucose) and they diffuse down a concentration gradient on the other side of the epithelial cell (ion channel for sodium, facilitated diffusion for glucose). These differences I just noted are basic and general differences between sodium and glucose transportation, and not specific for an epithelial cell. Has anyone got some differences that are substantial and solely defined to an epithelial cell?

Answer 1

Glucose can be transported across a biological membrane(i.e. epithelium)in the following ways:
1.Diffusion – very slow
2.Facilitated diffusion- via glucose carrier(protein that change shape to transport glucose across a membrane down their electrochemical gradient)
3.Secondary active transport: Na-glucose symporter, 2Na down the gradient for 1 glucose up the grad(no ATP-energy)

Na transport across epithelium:
1.diffusion
2.Na-glucuse/Chloride/Aminoacid co transport = secondary active transport as no ATP is used to pump Na against/with gradient
3.Calcium-Na antiporter = secondary active transport
4.Primary active transport as ATP’s are used to pump Na against the gradient

So I suppose the difference is only 4: primary active transport

Answer 2

In the upper intestine both sodium and water absorption are largely dependent on the presence of D-glucose. The link between active sodium transport and glucose is the coupled transport of sodium and glucose across the brush border membrane of enterocytes by the Na+/ glucose cotransporter (SGLT1). Na+ that enters the cells with glucose is pumped out towards the blood by 3Na+/2K+ pumps on the basolateral membrane, and glucose passes out across the basolateral membrane by facilitated diffusion, the net result being that glucose and sodium are transported across the epithelium. The coupling between Na+, glucose, and water transport is less well understood. It is commonly thought that Na+ transport increases the local osmotic pressure in the lateral intercellular spaces, and that this in turn generates osmotic water flow across the epithelium. Recent work suggests a more direct link between Na+, glucose, and water transport; that is, water is cotransported along with Na+ and sugar through SGLT1.