If the concentration of glucose in the blood exceeds the renal threshold for
glucose, usually 180 to 200 mg/dL, the kidneys may not reabsorb all of the
filtered glucose; the glucose then appears in the urine (glycosuria). When excess
glucose is excreted in the urine, it is accompanied by excessive loss of fluids and
electrolytes. This is called osmotic diuresis.
Because insulin normally inhibits glycogenolysis (breakdown of stored glucose)
and gluconeogenesis (production of new glucose from amino acids and other
substrates), these processes occur in an unrestrained fashion in people with
insulin deficiency and contribute further to hyperglycemia. In addition, fat
breakdown occurs, resulting in an increased production of ketone bodies, which
are the byproducts of fat breakdown.Type 2 Diabetes Mellitus
- Accounts for 90% of patients with diabetes
- Usually occurs in people over 40 years of age
- 80-90% of patients are overweight
Etiology and Pathophysiology
- Pancreas continues to produce some endogenous insulin
- Insulin produced is either insufficient or poorly utilized by the tissues
- Insulin resistance
- Body tissues do not respond to insulin
- Results in hyperglycemia
- Inappropriate glucose production by the liver
- Not considered a primary factor in the development of type 2 diabetes
Normally, insulin binds to special receptors on cell surfaces and initiates a series of
reactions involved in glucose metabolism. In type 2 diabetes, these intracellular
reactions are diminished, making insulin less effective at stimulating glucose
uptake by the tissues and at regulating glucose release by the liver. The exact mechanisms that lead to insulin resistance and impaired insulin secretion
in type 2 diabetes are unknown, although genetic factors are thought to play a role. To overcome insulin resistance and to prevent the buildup of glucose in the blood,
increased amounts of insulin must be secreted to maintain the glucose level at a
normal or slightly elevated level. However, if the beta cells cannot keep up with
the increased demand for insulin, the glucose level rises, and type 2 diabetes
develops.