A 45-year-old morbidly obese woman has been attempting to lose weight using a low- carbohydrate diet. After 2 months of little success, she confides in her son that she does add glucose to her coffee in the morning and after dinner but feels only some of this will be absorbed and should not be the cause of her limited success. Her son, a medical student, states that glucose is almost completely absorbed from the gut. What type of transport does glucose utilize for gastro intestinal absorption?
A. Active- Carrier mediated, against the concentration gradient and energy dependent
B. Facilitated- Carrier mediated, down the concentration gradient
C. Passive- Down the concentration gradient
D. Active and facilitated
E. Passive and facilitated
Figure- showing the mechanism of absorption of glucose
There are two separate mechanisms for the Absorption of Monosaccharides in the Small Intestine (figure) Glucose and galactose are absorbed by a sodium-dependent process. They are carried by the same transport protein (SGLT 1), and compete with each other for intestinal absorption. Other monosaccharides (mainly) including glucose (but to a lesser extent) are absorbed by carrier-mediated diffusion.
Fructose is mainly transported by Facilitated transport using GLUT-5 transporter. Because they are not actively transported, fructose and sugar alcohols are only absorbed down their concentration gradient, and after a moderately high intake, some may remain in the intestinal lumen, acting as a substrate for bacterial fermentation.
Glucose is a polar molecule; the passive diffusion across the intestinal membrane is very-very slow.
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