Final answer:
Gut epithelial cells use a symport mechanism for active transport of glucose against its concentration gradient, with energy from the Na+/K+ ATPase pump. Glucose moves from the intestinal lumen through epithelial cells, into interstitial space, and then into the bloodstream, finally reaching the liver via the hepatic portal vein.
Step-by-step explanation:
Gut epithelial cells facilitate the active transport of glucose from the intestinal lumen against its concentration gradient across the apical membrane. This is achieved through a symport mechanism where glucose and Na+ bind to carrier proteins, allowing their co-transport into the epithelial cells. Subsequently, glucose is transported into the interstitial space and ultimately into the bloodstream. The energy required for glucose transport is provided by the Na+/K+ ATPase that actively pumps Na+ out of the cell, maintaining the necessary concentration gradients.
The epithelial tissue lining the small intestine is highly specialized for absorption, with features such as villi and microvilli that greatly increase the surface area. Nutrients, including glucose, pass from the lumen through the epithelial cells and into the blood capillaries within the villi. The capillary blood then transports nutrients to the liver via the hepatic portal vein. It is important to note that water-soluble nutrients cannot pass between epithelial cells due to the presence of tight junctions, thus must be taken up into cells through specialized mechanisms like active transport and facilitated diffusion.