Absorption of glucose in small intestine is through
**Core Concept**
The absorption of glucose in the small intestine occurs through a specific transport mechanism that involves the binding of glucose molecules to a carrier protein on the luminal surface of intestinal epithelial cells. This process is facilitated by the presence of sodium ions and the enzyme sodium-glucose cotransporter 1 (SGLT1).
**Why the Correct Answer is Right**
The correct answer involves the sodium-glucose cotransporter 1 (SGLT1), which is a member of the SLC5A family of proteins. SGLT1 is a secondary active transporter that uses the electrochemical gradient of sodium ions to drive the uptake of glucose molecules into the intestinal epithelial cells. The binding of glucose to SGLT1 causes a conformational change that results in the transport of both sodium and glucose ions across the cell membrane. This process is essential for the efficient absorption of glucose from the intestinal lumen.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a transport mechanism for glucose absorption. While glucose does diffuse through the lipid bilayer to some extent, this process is not sufficient to account for the rapid and efficient absorption of glucose in the small intestine.
**Option B:** This option is incorrect because it refers to a different type of transport mechanism. The glucose-galactose transporter (SGLT2) is involved in the reabsorption of glucose in the renal proximal convoluted tubule, but it is not responsible for glucose absorption in the small intestine.
**Option C:** This option is incorrect because it refers to a passive diffusion process. While some substances can diffuse through the lipid bilayer, glucose is too large and polar to pass through the membrane in this way.
**Option D:** This option is incorrect because it refers to a different type of transport mechanism. The glucose transporter 2 (GLUT2) is involved in the transport of glucose across cell membranes in certain tissues, such as the liver and kidneys, but it is not responsible for glucose absorption in the small intestine.
**Clinical Pearl / High-Yield Fact**
The sodium-glucose cotransporter 1 (SGLT1) is a high-capacity, low-affinity transporter that is responsible for the majority of glucose absorption in the small intestine. This process is essential for the efficient uptake of glucose from the diet and is critical for maintaining normal blood glucose levels.
**Correct Answer:** C. Passive diffusion through the lipid bilayer is not a significant mechanism for glucose absorption in the small intestine.