Glucose is a monosaccharide, meaning it's a single sugar unit. In nature, glucose occurs either on its own or chemically bonded to other molecules of glucose or other monosaccharides. Many of the foods that humans eat contain glucose in one form or another, and glucose is an important source of nutrition for cells.
Cellular Energy
Your body cells need a source of energy -- to obtain energy, they burn nutritional molecules in oxygen. Most body cells use several different nutritional molecules for energy, including proteins, carbohydrates and fats. Some body cells, however, preferentially burn glucose, which is a carbohydrate. As such, glucose is a particularly important source of nutrition for cells, especially brain cells.
Sources of Glucose
You obtain glucose for the cells whenever you consume a carbohydrate composed of glucose or a combination of glucose and other monosaccharides. Examples of such carbohydrates include starch, which is made of pure glucose, and table sugar, which is made of a combination of glucose and the monosaccharide fructose, chemically linked together. You also ingest glucose when you consume fiber, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry," but you can't access this glucose, because you can't digest fiber.
Digestion and Absorption
Except in those instances in which you consume glucose as a monosaccharide -- some processed foods contain pure glucose, and high-fructose corn syrup is a source of monosaccharide glucose -- you must digest the carbohydrates you consume. Enzymes in your digestive tract break starches and sugars down into their constituent monosaccharides, explains Dr. Lauralee Sherwood in her book "Human Physiology," and you then absorb the monosaccharides into the bloodstream.
Glucose Uptake
For glucose to have any nutritional value, you can't just absorb it into the bloodstream -- you also have to move it into the cells. Cells take up glucose from the blood in response to the hormone insulin, which your pancreas releases when you consume a glucose-containing food. Insulin causes cells to take up glucose and either burn it for immediate energy or store it for later use, in the form either of carbohydrate or fat.
Metabolism
The nutritional value of glucose is its energy content -- your cells can burn it for calories. You accomplish this through a series of chemical reactions. Through these reactions, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry," your cells combine glucose with oxygen to produce the waste products carbon dioxide and water. This yields energy, which your cells can then use to produce various other products, communicate with one another, and generate movement.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
