Metabolism
Absorptive and post absorptive stage of metabolismThe body has two phases to its metabolic cycle. The first is known as the absorptive stage. This stage happens 3-4 hours after a typical meal. During this phase nutrients are absorbed by the body. In other words this is the stage where energy is stored into macromolecules. During the post-absorptive stage the nutrients are not being absorbed instead this is the stage where it is being mobilized.
Insulin
The changes in the body that occur between the absorptive and post-absorptive stages are triggered by the changes in the plasma concentration of insulin. Insulin encourages the synthesis of energy storage molecules. When plasma glucose levels in the bloodstream increase during the absorptive stage, insulin is secreted from the pancreas. When the plasma glucose levels decrease, the post-absorptive phase begins. Insulin acts on several different tissues in the body and influences almost every major aspect of energy metabolism. Insulin supports and promotes all aspects of the absorptive phase by helping store energy in all tissues. It also inhibits the reactions of the post-absorptive phase. Insulin also affects the transport of nutrients across the membrane of ALL body cells except for those located in the liver and CNS. Insulin also has a part in growth where it needs to be present in the blood stream in order for the hormones to effect normally. Epinephrine and sympathetic nervous activity on metabolism
The sympathetic system and epinephrine suppress insulin and stimulate glycogen secretion. This effects the post absorptive phase by making metabolic adjustments. During the post absorptive phase, plasma glucose levels decrease and cause an increase of glycogen secretion. It also acts directly on glucose receptors in the CNS. This causes a rise in epinephrine secretion by the adrenal medulla. The rise in epinephrine creates a cascade event where the body sends signals to all the tissues (except skeletal muscles) to switch to the post absorptive phase.
