Question

Discuss glucose transport in epithelial cells, include tight junctions in your discussion.

Answer 1

The transportation of glucose in epithelial cells occurs by two ways. One, includes Na+ dependent transportation and the other way emplyos the use of specialized glucose transporters named as GLUT.

1. The apical surface or the lumen surface of the small intestine bears the brush border epithellium, called microvilli, which imports the glucose against its concentration gradient. As a result, one glucose molecules enters inside the intestinal lumen along with 2 Na+ ions that establishes the symport mode of transportation. All the Na+ ions that are transported from the intestinal lumen are made to efflux to the basolateral side whichis mediated by the Na/K ATPase machinary. This mechanism also ensures the uphill transportation of glucose, as this machinary works by producing and hydrolysing the ATP.

2. Once the glucose is transported inside the lumen of the small intestine, it has to exit through the basolateral surface so that glucose could enter inside the blood stream. This is governed by the specialized transporter proteins called GLUT-2 which are present on the basolateral membrane.

** Tight junctions are present between the adjacent epithellial cells so that the glucose molecules does not diffuse back inside the intestinal lumen.