Glucose and lactose are carbohydrates and, more specifically, are sugars. In the body, both can be used as a source of cellular energy, though some individuals have difficulty digesting lactose, and are called "lactose intolerant." Other individuals -- those with diabetes -- can't take up glucose into the cells from the bloodstream.
Significance
From a chemical perspective, carbohydrates -- including glucose and lactose --are chemical compounds made up of carbon, hydrogen and oxygen. Some, including glucose and lactose, taste sweet, as they consist of only one or two individual sugar molecules. Other carbohydrates taste starchy, and are made up of many sugar molecules linked together. In the digestive tract, explains Dr. Lauralee Sherwood in her book "Human Anatomy," carbohydrates are broken down into their individual sugar molecules, which are absorbed, and then used by cells for energy.
Features
While fructose is a monosaccharide, or single sugar unit, note Doctors Mary Campbell and Shawn Farrell in their book "Biochemistry," lactose is a disaccharide, meaning it's made of two sugar units linked together. Specifically, lactose is made up of the two sugar units glucose and galactose, where galactose is a sugar very closely related to, but with a chemical structure slightly different than, glucose. Glucose can be absorbed from the intestine directly, while lactose must be broken into glucose and galactose before absorption.
Considerations
All humans have the ability to take up glucose from the intestine into the bloodstream, but there are some individuals who can't digest lactose. This, explain Doctors Reginald Garrett and Charles Grisham in their book "Biochemistry," is because some individuals lack the enzyme lactase. Enzymes are responsible for helping chemical reactions to take place faster than they otherwise would, and are necessary to separate the sugar units in lactose prior to absorption. Those without lactase are lactose intolerant.
Effects
Once glucose or the constituents of lactose -- glucose and galactose -- are in the bloodstream, they're taken up by cells. Glucose requires the intervention of a chemical "gatekeeper" molecule for cells to take it up from the blood. Specifically, explains Sherwood, the pancreas must release the hormone insulin, which travels throughout the body and binds to receptors on cells. Diabetics don't produce or can't respond to insulin, meaning that they are unable to take up glucose from the bloodstream.
Expert Insight
Problems absorbing or metabolizing sugars can lead to symptoms. In lactose intolerant individuals, undigested lactose travels to the lower intestine, where it's digested by bacteria who produce large quantities of gas as byproducts of metabolism. This leads to the cramping associated with lactose intolerance, explain Garrett and Grisham. Diabetics, after eating glucose, will have very high blood sugar. Some diabetics can treat this with injected insulin, but untreated high blood sugar leads to serious complications, including coma and death.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
