碳水化合物的新陈代谢

Salivary amylase enzymes break down starch into smaller polymers as soon as food enters the mouth. This initial breakdown is crucial because amylase enzymes cannot function in the stomach's acidic environment. The partially digested starch then travels to the small intestine, where pancreatic amylases continue breaking it down into disaccharides like maltose and dextrin.

Brush-border cells of the small intestine secrete specific enzymes that metabolize disaccharides into monosaccharides. Beta-galactosidase breaks lactose into glucose and galactose, while sucrase hydrolyzes sucrose into glucose and fructose. These monosaccharides are then transported across the intestinal epithelium into the bloodstream for absorption by body cells.

Once inside a cell, glucose enters glycolytic pathways where it is metabolized into pyruvate. This process is coupled with the production of energy molecules ATP and NADH. The role of reduced coenzymes NADH and FADH in energy production makes this process essential for cellular energy generation.

Galactose and fructose are converted to glucose-6-phosphate after absorption into body cells. Once converted, they enter glycolysis alongside glucose. This conversion allows these monosaccharides to participate in the same energy-producing metabolic pathways as glucose, ensuring efficient energy extraction from all dietary carbohydrates.

Humans lack cellulase, the enzyme required to digest cellulose found in plant cell walls. Although cellulose cannot be broken down for energy, it provides dietary fiber that adds bulk to food and aids digestion by helping partially digested food move smoothly through the intestines.

Type 2 diabetes develops when cells become resistant to insulin effects. In response, the pancreas increases insulin secretion, but beta cells eventually become exhausted. Lifestyle factors such as poor diet, inactivity, and obesity greatly increase risk. In many cases, moderate weight loss, regular physical activity, and healthy diet can reverse the condition.

Normal blood glucose levels range from 70-99 mg/dL. Any deviation from this range signals poor carbohydrate metabolism and a weak regulatory system. Dysfunction in insulin production, secretion, or target cell responsiveness can lead to diabetes mellitus, a condition affecting millions of adults and children in the United States.