Question

Glucose from digested food enters intestinal epithelial cells by active transport. Why would intestinal cells use active transport when most body cells use facilitated diffusion?

Answer 1

Glucose enters intestinal epithelial cells by active transport because the cell membranes are impermeable to water-soluble nutrients like glucose. Substances cannot pass between epithelial cells of the intestinal mucosa, so active transport is needed for glucose to enter the bloodstream. Active transport is necessary to move glucose against its concentration gradient.

Step-by-step explanation:

Glucose from digested food enters intestinal epithelial cells by active transport because the cell's plasma membrane is made up of hydrophobic phospholipids, and water-soluble nutrients like glucose cannot pass through by simple diffusion. Furthermore, substances cannot pass between the epithelial cells of the intestinal mucosa because these cells are bound together by tight junctions.

Therefore, to enter the bloodstream, glucose and other water-soluble nutrients must be actively transported across the apical surfaces of epithelial cells and into the interstitial fluid, where they can enter the capillary blood.

Answer 2

Glucose is usually transported by co-transport mechanism along with sodium ions.

Step-by-step explanation:

Glucose cannot be absorbed if there is no sodium transport through the intestinal membrane. Glucose is transported by co-transport mechanism with the active transport of sodium. The transport of sodium occurs in two steps:

- First is the active transport of sodium which occurs across the basolateral membrane of intestinal cells into the paracellular spaces. This results in depletion of sodium inside the intestinal epithelial cells.

-Second is the facilitated diffusion of sodium from intestinal lumen to intestinal epithelial cells. For this sodium combines with a transport protein but the protein will not transport until it binds with glucose. Thus both sodium and glucose are co-transported by the transport protein. Once glucose is inside the epithelial cells of intestine, it is moved to the para-cellular spaces by facilitated diffusion. Thus it is the initial active transport of sodium which gives the motive force for the transport of glucose through the membranes.