What is diabetes?
The two major forms of diabetes are type 1 (previously
called Insulin Dependent Diabetes Mellitus (IDDM) or
juvenile-onset diabetes) and type 2 (previously called
Non Insulin Dependent Diabetes Mellitus (NIDDM) or maturity-onset
diabetes).
Insulin
-
Diabetes type 1 and type 2 share
one central feature: elevated blood sugar (glucose)
levels due to absolute or relative insufficiencies
of insulin, a hormone produced by the pancreas.
Insulin is a key regulator of the body's metabolism.
It normally works in the following way:
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During and immediately after a
meal the process of digestion breaks carbohydrates
down into sugar molecules (of which glucose
is one) and proteins into amino acids.
-
Right after the meal, glucose and
amino acids are absorbed directly into the bloodstream,
and blood glucose levels rise sharply. (Glucose
levels after a meal are called postprandial
levels.)
-
The rise in blood glucose levels
signals important cells in the pancreas, called
beta cells, to secrete insulin, which pours
into the bloodstream. Within ten minutes after a
meal insulin rises to its peak level.
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Insulin then enables glucose and
amino acids to enter cells in the body, particularly
muscle and liver cells. Here, insulin and other
hormones direct whether these nutrients will be
burned for energy or stored for future use. (It
should be noted that the brain and nervous system
are not dependent on insulin; they regulate their
glucose needs through other mechanisms.)
-
When insulin levels are high, the
liver stops producing glucose and stores it in other
forms until the body needs it again.
-
As blood glucose levels reach their
peak, the pancreas reduces the production of insulin.
-
About two to four hours after a
meal both blood glucose and insulin are at low levels,
with insulin being slightly higher. The blood glucose
levels are then referred to as fasting blood
glucose concentrations .
Type 1 Diabetes
In type 1 diabetes, the disease process
is more severe and onset is usually in childhood:
- Beta cells in the pancreas that produce insulin
are gradually destroyed. Eventually insulin deficiency
is absolute.
-
Without insulin to move glucose
into cells, blood glucose levels become excessively
high, a condition known as hyperglycemia.
-
Because the body cannot utilize
the sugar, it spills over into the urine and is
lost.
-
Weakness, weight loss, and excessive
hunger and thirst are among the consequences of
this "starvation in the midst of plenty."
Patients become dependent on administered
insulin for survival
Type 2 Diabetes
Type 2 Diabetes is most common form
of diabetes, accounting for 90% of cases. An estimated
16 million Americans have type 2 diabetes and half are
unaware they have it. The disease mechanisms in type
2 diabetes are not wholly known, but some experts suggest
that it may involve the following three stages in most
patients:
-
The first stage in type 2 diabetes is the condition
called insulin resistance; although insulin
can attach normally to receptors on liver and
muscle cells, certain mechanisms prevent insulin
from moving glucose (blood sugar) into these cells
where it can be used. Most type 2 diabetics produce
variable, even normal or high, amounts of insulin,
and in the beginning this amount is usually sufficient
to overcome such resistance.
-
Over time, the pancreas becomes unable to produce
enough insulin to overcome resistance. In type
2 diabetes the initial effect of this stage is
usually an abnormal rise in blood sugar right
after a meal (called postprandial hyperglycemia
). This effect is now believed to be particularly
damaging to the body.
-
Eventually, the cycle of elevated glucose further
impairs and possibly destroys beta cells, thereby
stopping insulin production completely and causing
full-blown diabetes. This is made evident by fasting
hyperglycemia , in which elevated glucose
levels are present most of the time.
Maturity-Onset Diabetes in Youth.
Maturity-onset diabetes in youth (MODY) is a rare
genetic form of type 2 diabetes that develops only in
Caucasian teenagers. It accounts for 2% to 5% of type
2 cases.
Gestational Diabetes. An estimated 5% of pregnant
women develop a form of type 2 diabetes, usually temporary,
in their third trimester called gestational diabetes.
Diabetes Secondary to Other Conditions
Conditions that damage or destroy the
pancreas, such as pancreatitis, pancreatic surgery,
or certain industrial chemicals can cause diabetes.
Certain drugs can also cause temporary diabetes, including
corticosteroids, beta-blockers, and phenytoin. Rare
genetic disorders (Klinefelter's syndrome, Huntington's
chorea, Wolfram's syndrome, leprechaunism, Rabson-Mendenhall
syndrome, lipoatrophic diabetes, and others) and hormonal
disorders (Acromegaly, Cushing's syndrome, pheochromocytoma,
hyperthyroidism, somatostatinoma, aldosteronoma) also
increase the risk for diabetes. |