The rate of absorption of sugars by the small intestine is highest for?
**Core Concept**
The rate of absorption of sugars by the small intestine is influenced by the molecular structure and the presence of specific transport mechanisms. The small intestine utilizes both passive diffusion and active transport to absorb various sugars, including glucose, fructose, and galactose.
**Why the Correct Answer is Right**
Glucose is absorbed by the small intestine primarily through facilitated diffusion via the sodium-glucose cotransporter 1 (SGLT1) in the enterocytes. This transport mechanism has a high affinity for glucose and is capable of transporting glucose against its concentration gradient, resulting in a rapid rate of absorption. The presence of SGLT1 in the small intestine allows for the efficient absorption of glucose, which is essential for maintaining normal blood glucose levels.
**Why Each Wrong Option is Incorrect**
**Option A:** Fructose is absorbed by facilitated diffusion via GLUT5, but it does not have the same high-affinity transport mechanism as glucose, resulting in a slower rate of absorption.
**Option B:** Galactose is absorbed by facilitated diffusion via GLUT2, but it is not absorbed as rapidly as glucose due to its lower affinity for the transporter.
**Option D:** Lactose is a disaccharide composed of glucose and galactose, and its absorption is slower than that of glucose due to the need for hydrolysis by lactase enzyme before absorption.
**Clinical Pearl / High-Yield Fact**
The small intestine's ability to absorb glucose is essential for maintaining normal blood glucose levels, and impaired glucose absorption can lead to conditions such as glucose malabsorption and diarrhea.
**Correct Answer:** C. Glucose