Blood Sugar Regulation - Biology Encyclopedia - cells, body, function, human, system, life, hormone, used, structure
Blood Sugar Regulation - Biology Encyclopedia
Blood Sugar Regulation
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Most cells in the human body use the sugar called glucose as their major source of energy. Glucose molecules are broken down within       cells in order to produce adenosine triphosphate (ATP) molecules,       energy-rich molecules that power numerous cellular processes. Glucose       molecules are delivered to cells by the circulating blood and therefore,       to ensure a constant supply of glucose to cells, it is essential that       blood glucose levels be maintained at relatively constant levels. Level       constancy is accomplished primarily through negative feedback systems, which ensure that blood glucose concentration is maintained       within the normal range of 70 to 110 milligrams (0.0024 to 0.0038 ounces)       of glucose per deciliter (approximately one-fifth of a pint) of blood.
Negative feedback systems are processes that sense changes in the body and activate mechanisms that       reverse the changes in order to restore conditions to their normal levels.       Negative feedback systems are critically important in homeostasis, the       maintenance of relatively constant internal conditions. Disruptions in       homeostasis lead to potentially life-threatening situations. The       maintenance of relatively constant blood glucose levels is essential for       the health of cells and thus the health of the entire body.
Major factors that can increase blood glucose levels include glucose       absorption by the small intestine (after ingesting a meal) and the       production of new glucose molecules by liver cells. Major factors that can       decrease blood
The homeostatic regulation of glucose concentrations.
glucose levels include the transport of glucose into cells (for use as a       source of energy or to be stored for future use) and the loss of glucose       in urine (an abnormal event that occurs in diabetes mellitus).
Insulin and Glucagon
In a healthy person, blood glucose levels are restored to normal levels       primarily through the actions of two pancreatic hormones , namely insulin and glucagon. If blood glucose levels rise (for example,       during the fed or absorptive state, when a meal is digested and the       nutrient molecules are being absorbed and used), the beta cells of the       pancreas respond by secreting insulin. Insulin has several notable       effects: (1) it stimulates most body cells to increase their rate of       glucose uptake (transport) from the blood; (2) it increases the cellular       rate of glucose utilization as an energy source; (3) it accelerates the       formation of glycogen from glucose in liver and skeletal muscle cells; and (4) it stimulates       fat synthesis (from glucose) in liver cells and adipose (fat) tissue.       These effects collectively cause a decrease in blood glucose levels back       to normal levels.
If blood glucose levels fall below normal levels (for instance, during the       post-absorptive or fasting state, when nutrients from a recently digested       meal are no longer circulating in the blood, or during starvation),       insulin secretion is inhibited and, at the same time, the alpha cells of the pancreas       respond by secreting glucagon, a hormone that has several important       effects:         (1) it accelerates the breakdown of glycogen to glucose in liver and       skeletal muscle cells; (2) it increases the breakdown of fats to fatty       acids and glycerol in adipose tissue and, consequently, the release of       these substances into the blood (which cells can thus use for energy); and       (3) it stimulates liver cells to increase glucose synthesis (from glycerol       absorbed from the blood) and glucose release into the blood. These effects       collectively cause an increase in blood glucose levels back to normal       levels.
In addition to insulin and glucagon, there are several other hormones that       can influence blood glucose levels. The most important ones are       epinephrine, cortisol, and growth hormone, all of which can increase blood       glucose levels.
Diseases and Blood Sugar Regulation
Glucose levels above or below the normal range are indicative of the       presence of disease states. For example, elevated glucose levels are       present in diabetes mellitus, Cushing's syndrome, liver disease,       and hyperthyroidism, while decreased glucose levels are present in       Addison's disease, hyperinsulinism, and hypothyroidism.
The most prevalent of these diseases is diabetes mellitus. There are two       types of this disease: Type I (insulin-dependent or juvenile-onset)       diabetes mellitus, and Type II (noninsulin-dependent or maturity-onset)       diabetes mellitus. In Type I diabetes, pancreatic beta cells are destroyed       by an erroneous attack by the body's own immune system, and thus       insulin secretion is reduced to negligible levels. In Type II diabetes,       insulin secretion is not reduced; however, there is a reduced sensitivity       of target cells to insulin, a phenomenon known as insulin resistance.
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