 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. It is the
production of insulin and glucagon by the pancreas which determines if a
patient has diabetes,
hypoglycemia.
Insulin
and glucagon are hormones secreted by islet cells within the pancreas.
They are both secreted in response to blood sugar levels, but in opposite
fashion! (antagonists)
Insulin
is secreted by the beta 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.
http://www.endocrineweb.com/insulin.html
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