Digestion and Metabolism
Ingested carbohydrates (polysaccharides and disaccharides) are broken down into their monosaccharide components (e.g. glucose and fructose) free for absorption. Both glucose and fructose cross the intestinal lining through distinct complex transporters into the bloodstream of the hepatic portal system, which carries the monosaccharides to the liver for further processing. After absorption, glucose and fructose follow different metabolic pathways.
Glucose, is the primary source of energy to nearly every cell in the body. It circulates within the bloodstream until the hormone insulin facilitates its uptake into cells.
Within the cell, glucose is converted to pyruvate through glycolysis; Pyruvate can then enter either aerobic or anaerobic respiration to produce energy for the cell metabolism. In the cytoplasm of cells containing mitochondria the process is aerobic and more efficient. As red blood cells don't have mitochondria, anaerobic metabolism of glucose into energy is moderately efficient.