Absorptive and Postabsorptive States The absorptive state is the time during and right after eating a meal. The absorptive state lasts for four hours, during and after each meal. During this state glucose is the most important energy fuel. Amino acids and fats are used to form degraded protein, and small amounts are used to provide ATP. Metabolites are transformed to fat if they are not used for anabolism. Glucose is formed by the conversion of fructose and galactose, which are stored in the liver from the entrance of monosaccharides. Glucose is released into the blood, or converted to glycogen and fat. Some glucose enters the liver and is used for energy, and any that is not used will be stored in skeletal muscle as glycogen or in adipose cells as fat. Liver, skeletal muscle, and adipose cells use triglycerides as their primary energy source. Amino acid are also used by the liver to synthesize plasma proteins. Essentially all of the events that occur in the absorptive state are directed by insulin. The postabsorptive state is the period when the GI tract is empty and energy comes from the breakdpwn of our bodys reserves. The importance of the postabsorptive state is to maintain blood glucose levels. The brain fuels itself using glucose as its energy source. We can get glucose from stored glycogen, tissue proteins, and some from fats. The first available store of glucose is in the livers stores of glycogen. These stores can maintain blood sugar levels for around four hours. When the liver stores begin to get small, glycogenolysis begins to take place in skeletal muscles. The glucose in the skeletal muscles is converted to pyruvic acid, which enters the blood and is converted back to glucose by the liver and again reenters the blood. In adipose tissue glycerol is produced and the liver converts it to glucose. The postabsorptive stat is controlled by the intervention of the sympathetic nervous system and the hormo...
