the major carbohydrate that tissue cells use as fuel is
Carbohydrate metabolism Although humans consume a variety of carbohydrates, digestion breaks down complex carbohydrates into a few simple monomers for metabolism: glucose, fructose, and galactose.[4] Glucose constitutes about 80% of the products, and is the primary structure that is distributed to cells in the tissues, where it is broken down or stored as glycogen.[3][4] In aerobic respiration, the main form of cellular respiration used by humans, glucose and oxygen are metabolized to release energy, with carbon dioxide and water as byproducts.[2] Most of the fructose and galactose travel to the liver, where they can be converted to glucose.[4]
Glycogen Approximately 4Â grams of glucose are present in the blood of humans at all times;[2] in fasted individuals, blood glucose is maintained constant at this level at the expense of glycogen stores in the liver and skeletal muscle.[2] Glycogen stores in skeletal muscle serve as a form of energy storage for the muscle itself;[2] however, the breakdown of muscle glycogen impedes muscle glucose uptake, thereby increasing the amount of blood glucose available for use in other tissues.[2] Liver glycogen stores serve as a store of glucose for use throughout the body, particularly the central nervous system.[2] The human brain consumes approximately 60% of blood glucose in fasted, sedentary individuals.[2]