glucose absorption

[farahnaazf88]

What type of cells use Na dependant glucose simporter?

[farahnaazf88]

Why do liver cells use facilitated diffusion? Doesn't facilitated take a long time to transport material.

[MrMistery]

farahnaaz,
There are different places where glucose/Na symporter is used, and as I said before different symporters, but general this type of system is used when you want to concentrate glucose and the glucose gradient is not the way you want it to be. That is why the cell then couples uptake of glucose with the uptake of sodium which is (almost) always in much higher concentration in the extracellular space than in the cell. The classic examples of cells using Na/glucose symporters are enterocytes and cells of the proximal tubule of the tubule, but there may be other cells where this particular transporter is expressed.

As for your second question: I don't exactly what the kinetics of these particular two types of transporters are, but generally secondary active transport proteins(like the glucose/Na symporter) work about as fast as ping-pong uniporters(like the GLUT family of permeases). What you are probably thinking about is ion channels. Indeed, these proteins allow for much more rapid of a transport across a membrane, but of course this does not apply to our case.

Cheers.

[farahnaazf88]

thankyou