Glucose is a simple sugar molecule, known as a monosaccharide. Almost all the carbohydrates that you consume are broken down into their simplest form, glucose, before they are absorbed and used by the body. All of your cells run on glucose; in fact, energy cannot be produced without this molecule. Different factors influence the transport of glucose into the blood and the cells including hormones, physical activity and disease.
Digestion and Absorption
Digestion of carbohydrates into glucose begins in the mouth. Salivary amylase is an enzyme that begins to break down carbohydrates as soon as you chew. Digestion pauses in the stomach then finishes in the small intestine. Once glucose is present inside the small intestine it is moved into your bloodstream by sodium-glucose transport proteins that work through active transport to move glucose into the extracellular fluid and into the blood where it can be used.
Glucose Transport
When glucose enters your bloodstream, your pancreas is triggered and releases the hormone insulin. This hormone's primary role is to move glucose from your bloodstream and into cells for use or for storage. The method your body uses is simple and effective. Your cells have an insulin receptor that triggers a glucose transporter to move to the outside of the cell. When the insulin connects with the receptor, the glucose transporter is activated and begins to move glucose from the blood and into the cell.
During Exercise
The effect of exercise on glucose transportation is much like that during the presence of insulin. When your muscles contract in a rhythmic manner like during exercise, it triggers your glucose transporters to move toward the outer layer of the cell. When this occurs, your cell begins bringing in glucose from the blood for use during exercise. It is said that exercise has an insulin-like effect on blood glucose.
Problems
The movement of glucose from the blood and into the cells is not always without flaw. Diabetes is a condition in which the body does not respond to the presence of insulin. This means that glucose cannot easily move from the bloodstream and into the cells. Usually this occurs when the cells no longer recognize and respond to insulin. However, exercise is still effective to move glucose into the cells in diabetics.
References
- "Nutrition: Concepts and Controversies"; Frances Sizer and Eleanor Whitney; 2004
- "Anatomy and Physiology"; Kenneth S. Saladin; 2004
- Colorado State University; Physiologic Effects of Insulin; R. Bowen; August 2009
- "Exercise Physiology"; George A. Brooks, Thomas D. Fahey, Kenneth M. Baldwin; 2005
- "Endocrinology and Metabolism"; Exercise Regulation of Glucose Transport in Skeletal Muscle; Tatsuya Hayashi, et al.; December 1997
- American Diabetes Association: Type 2 Diabetes
