Glucose, commonly called blood sugar, is one of the most ubiquitous of biomolecules in nature. Humans ingest glucose in several forms and use the molecule to provide energy to cells. Table sugar and starch are both sources of glucose. Adrenaline, a hormone released by the adrenal glands, can affect blood concentrations of glucose.
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Adrenaline, also known by the scientific name epinephrine, is a hormone that's responsible for the "fight or flight" response that occurs under conditions of excitement or imminent danger. One of the major effects of adrenaline is to increase the power of muscular contraction, in skeletal muscle and in the heart. In the case of the heart muscle, adrenaline also increases the heart rate, explains Dr. Lauralee Sherwood in her text, "Human Physiology." For muscles to contract, they must have an energy source such as glucose.
Glucose is found many places in the body. The significance of adrenaline relative to glucose is that it causes increased body demand for glucose so that muscles have plenty of glucose available to them in the presence of the stimulating influence of adrenaline. Generally, the amount of glucose in the bloodstream isn't sufficient to provide the necessary fuel for the muscles under conditions in which the adrenal glands have released adrenaline, explains Dr. Sherwood.
One of the roles of adrenaline is to promote the release of glucose from the locations in the body where it's stored. Skeletal muscles--those that promote movement and that humans can contract at will--store glucose, as does the liver. In their book "Biochemistry," Drs. Reginald Garrett and Charles Grisham explain that the muscles and liver store glucose in the form of a long chain of glucose molecules, called glycogen. Released adrenaline causes the liver and muscles to break down glycogen into glucose.
One of the benefits of the relationship between glucose and adrenaline is that while adrenaline directs the liver to break down glycogen and release glucose into the bloodstream, it directs muscle tissue somewhat differently. Because muscles need lots of glucose under the influence of adrenaline, the hormone directs muscles to break down glycogen into glucose. But instead of releasing that glucose, the muscles hold on to it and use it for immediate energy, note Drs. Garrett and Grisham.
The relationship between adrenaline and glucose is crucial to survival. Drs. Mary Campbell and Shawn Farrell explain in their book "Biochemistry" that although there are many fuel molecules that the body cells can use, under emergency situations, glucose is the best fuel. As such, adrenaline provides the best possible fuel for muscles in emergencies. Glucose makes an excellent emergency fuel because the cells can burn glucose even under conditions of low oxygen--such as when a person is running from a threat, and struggling to get enough air.