Which of the following statements regarding glucose absorption is true?
Glucose is absorbed mostly through the lining of the small intestine.
Glucose is absorbed solely through the lining of the mouth: the oral mucosa.
Glucose is absorbed mostly in the stomach.
Glucose is digested in the small intestine.
The Correct Answer and Explanation is:
Correct Answer:
Glucose is absorbed mostly through the lining of the small intestine.
Explanation:
Glucose absorption is a crucial part of human digestion and energy metabolism. The correct statement is that glucose is absorbed mostly through the lining of the small intestine, specifically in the jejunum and ileum portions. This process involves specialized mechanisms and structures that maximize the efficiency of nutrient uptake.
Digestion and Absorption Overview:
Carbohydrates in the diet are primarily in the form of polysaccharides (like starch) and disaccharides (like sucrose and lactose). The digestive process begins in the mouth, where the enzyme salivary amylase starts breaking down starch into maltose. However, very little actual absorption of glucose occurs in the mouth or stomach. The stomach primarily acts as a mixing and holding chamber, with minimal nutrient absorption.
Once the partially digested carbohydrates reach the small intestine, pancreatic amylase continues the breakdown of starch into simple sugars, mainly glucose, fructose, and galactose. Enzymes located on the brush border of the intestinal epithelial cells (like maltase, sucrase, and lactase) finish breaking down disaccharides into monosaccharides.
Absorption Mechanism:
Glucose is absorbed across the intestinal epithelium by a process called secondary active transport. It enters the epithelial cells via the SGLT-1 (sodium-glucose linked transporter-1), which requires the presence of sodium ions. Once inside the cell, glucose exits into the bloodstream through GLUT2 transporters on the basolateral membrane.
This absorption occurs efficiently in the small intestine, particularly in the duodenum and jejunum, because the mucosal surface is highly folded and contains villi and microvilli, increasing surface area for absorption.
In Summary:
- Glucose is not absorbed in the mouth or stomach.
- The small intestine is the primary site for glucose absorption.
- Specialized transport proteins facilitate the uptake of glucose into the bloodstream for energy use.