Absorption of monosaccharides in the small intestine involves a coordinated process where sugars such as glucose, galactose, and fructose are transported across the epithelial cells lining the intestines. After these sugars are absorbed at the apical membrane, they must exit the enterocytes at the basolateral membrane to enter the bloodstream and supply the body’s tissues.

Monosaccharide Transporters in Intestinal Epithelium

• Apical Membrane:
  At the brush border of the intestinal epithelial cells, glucose and galactose are absorbed primarily via the sodium-dependent glucose transporter 1 (SGLT1), whereas fructose is taken up through GLUT5.

• Basolateral Membrane:
  The exit of glucose and galactose from enterocytes into the blood is predominantly mediated by Glucose Transporter 2 (GLUT2). GLUT2 facilitates passive transport of these sugars down their concentration gradient out of the cells.

• GLUT3, GLUT4, and GLUT5:

  • GLUT3 is mainly found in neurons and is not involved in intestinal sugar exit.

  • GLUT4 is an insulin-regulated transporter primarily in muscle and adipose tissues.

  • GLUT5, as mentioned, facilitates fructose uptake at the apical membrane, not sugar exit.

Role of GLUT2

GLUT2 is a key transporter located basolaterally on enterocytes, ensuring the absorbed glucose and galactose efficiently pass into the bloodstream to maintain normal blood glucose levels. In certain conditions like high luminal glucose concentration, GLUT2 may transiently be recruited to the apical membrane to assist higher rates of glucose absorption.

Summary Table: Transporters and Their Functions in Monosaccharide Absorption

Conclusion

The transporter responsible for the exit of absorbed monosaccharides such as glucose and galactose from intestinal epithelial cells into the bloodstream is GLUT2. This transporter performs facilitated diffusion at the basolateral membrane, completing the absorption process.

Therefore, the correct answer is:
(1) GLUT2