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Diabetes mellitus, often simply diabetes is a syndrome characterized by
disordered metabolism and inappropiately high blood sugar
(hyperglycemia) resulting from either low levels of the hormone insulin
or from abnormal resistance to insulin's effects coupled with inadequate
levels of insulin secretion to compensate. The characteristic symptoms
are excessive urine production (polyuria), excessive thirst and
increased fluid intake (polydipsia), and blurred vision; these symptoms
may be absent if the blood sugar is mildly elevated.
The World Health Organization recognizes three main forms of diabetes
mellitus: type 1, type 2, and gestational diabetes (occurring during
pregnancy), which have similar signs, symptoms, and consequences, but
different causes and population distributions. Ultimately, all forms are
due to the beta cells of the pancreas being unable to produce sufficient
insulin to prevent hyperglycemia. Type 1 diabetes is usually due to
autoimmune destruction of the pancreatic beta cells, which produce
insulin. Type 2 diabetes is characterized by insulin resistance in
target tissues, but some impairment of beta cell function is necessary
for its development. Gestational diabetes is similar to type 2 diabetes,
in that it involves insulin resistance; the hormones of pregnancy can
cause insulin resistance in women genetically predisposed to developing
this condition.
Gestational diabetes typically resolves with delivery of the child,
however types 1 and 2 diabetes are chronic conditions. All types have
been treatable since insulin became medically available in 1921. Type 1
diabetes, in which insulin is not secreted by the pancreas, is directly
treatable only with injected or inhaled insulin, although dietary and
other lifestyle adjustments are part of management. Type 2 may be
managed with a combination of dietary treatment, tablets and injections
and, frequently, insulin supplementation. While insulin was originally
produced from natural sources such as porcine pancreas, most insulin
used today is produced through genetic engineering, either as a direct
copy of human insulin, or human insulin with modified molecules that
provide different onset and duration of action. Insulin can also be
delivered continuously by a pump surgically embedded under the skin.
Diabetes can cause many complications. Acute complications
(hypoglycemia, ketoacidosis or nonketotic hyperosmolar coma) may occur
if the disease is not adequately controlled. Serious long-term
complications include cardiovascular disease (doubled risk), chronic
renal failure, retinal damage (which can lead to blindness), nerve
damage (of several kinds), and microvascular damage, which may cause
impotence and poor healing. Poor healing of wounds, particularly of the
feet, can lead to gangrene, which may require amputation. Adequate
treatment of diabetes, as well as increased emphasis on blood pressure
control and lifestyle factors (such as not smoking and keeping a healthy
body weight), may improve the risk profile of most aforementioned
complications. In the developed world, diabetes is the most significant
cause of adult blindness in the non-elderly, the leading cause of
non-traumatic amputation in adults, and diabetic nephropathy is the main
illness requiring renal dialysis.
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