)Glucose, a
simple monosaccharide sugar, is one of the most important carbohydrates and is
used as a source of energy in animals and plants. Glucose is one of the main
products of photosynthesis and starts respiration. The natural form (D-glucose)
is also referred to as dextrose, especially in the food industry.
In respiration, through a series of enzyme-catalysed reactions, glucose is
oxidized to eventually to form carbon dioxide and water, yielding energy, mostly
in the form of ATP.
Chemically joined together, glucose and fructose form sucrose. Starch,
cellulose, and glycogen are common glucose polymers (polysaccharides).
The older name dextrose arose because a solution of D-glucose rotates polarised
light towards the right. In the same vein D-fructose was called "levulose"
because a solution of levulose rotates polarised light to the left.
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Normal Regulation of Blood Glucose
The important roles of insulin and glucagon: Diabetes and Hypoglycemia
The human body wants blood glucose (blood sugar) maintained in a very narrow
range. Insulin and glucagon are the hormones which make this happen. Both
insulin and glucagon are secreted from the pancreas, and thus are referred to as
pancreatic endocrine hormones. The picture on the left shows the intimate
relationship both insulin and glucagon have to each other. Note that the
pancreas serves as the central player in this scheme. It is the production of
insulin and glucagon by the pancreas which ultimately determines if a patient
has diabetes, hypoglycemia, or some other sugar problem.
Insulin and glucagon are hormones secreted by islet cells within the pancreas
(more about islet cells of the pancreas). They are both secreted in response to
blood sugar levels, but in opposite fashion!
Insulin is normally secreted by the beta cells (a type of islet cells) of the
pancreas. The stimulus for insulin secretion is a HIGH blood glucose...its as
simple as that! Although there is always a low level of insulin secreted by the
pancreas, the amount secreted into the blood increases as the blood glucose
rises. Similarly, as blood glucose falls, the amount of insulin secreted by the
pancreatic islets goes down. As can be seen in the picture, insulin has an
effect on a number of cells, including muscle, red blood cells, and fat cells
(shown in the picture). In response to insulin, these cells absorb glucose out
of the blood, having the net effect of lowering the high blood glucose levels
into the normal range.
Glucagon is secreted by the alpha cells of the pancreatic islets in much the
same manner as insulin...except in the opposite direction. If blood glucose is
high, then no glucagon is secreted. When blood glucose goes LOW, however, (such
as between meals, and during exercise), more and more glucagon is secreted. Like
insulin, glucagon has an effect on many cells of the body, but most notably the
liver. The effect of glucagon is to make the liver release the glucose it has
stored in its cells into the blood stream, with the net effect of increasing
blood glucose. Glucagon also induces the liver (and some other cells such as
muscle) to make glucose out of building blocks obtained from other nutrients
found in the body (e.g., protein).
Our bodies desire blood glucose to be maintained between 70 mg/dl and 110 mg/dl
(mg/dl means milligrams of glucose in 100 milliliters of blood). Below 70 is
termed "hypoglycemia". Above 110 can be normal if you have eaten within 2 to 3
hours. That is why your doctor wants to measure your blood glucose while you are
fasting...it should be between 70 and 110. Even after you have eaten, however,
your glucose should be below 180. Above 180 is termed "hyperglycemia" (which
translates to mean "too much glucose in the blood"). If you have two blood sugar
measurements above 200 after drinking a sugar-water drink (glucose tolerance
test), then you are diagnosed with diabetes. We have many pages on diabetes
which go into this in much more detail.
(From www.endocrineweb.com)
