Diabetes mellitus is a complex metabolic disease, characterized by either relative or absolute insulin deficiency. Insulin is a peptide hormone that is secreted by small clusters of cells (islets) in the pancreas. Insulin stimulates the uptake of glucose by peripheral target cells and regulates essential metabolic activities.

The two most common forms of diabetes are referred to as Type I and Type II. Type I is also called insulin-dependent or juvenile-onset diabetes. Type II is also called non-insulin-dependent or maturity-onset diabetes. Patients may present with weight loss, dehydration, polyuria, thirst (polydipsia), and increased appetite (polyphagia).

Type I diabetes typically occurs in children and adolescents, whereas Type II usually appears during the later decades of life (>30 years of age). Type II diabetes is far more common. About 10% of persons older than 65 years of age are afflicted with Type II diabetes. Most patients with Type II diabetes are overweight (80% of cases).

Complications of diabetes mellitus include infections, atherosclerosis, arteriosclerosis, nephropathy, retinopathy, and peripheral neuropathy. The development of these secondary lesions in diabetic patients is thought to be related to the severity and chronicity of hyperglycemia. Thus, control of blood glucose remains the most effective method for minimizing diabetic complications.

Here are the Key Points:

1. Type I diabetes is characterized by few if any functional beta cells in the islets of Langerhans and substantially reduced (or nonexistent) insulin secretion. As a result, body fat is metabolized as a source of energy. This produces ketone bodies and leads to metabolic acidosis. Lack of insulin results in hyperglycemia.

2. Hyperglycemia and glucosuria produce serious fluid and electrolyte imbalances, which can ultimately lead to coma and death. Before insulin became commercially available, Type I diabetes was usually fatal.

3. Type II diabetes refers to adult-onset hyperglycemia that reflects a failure of the beta cells to meet an increased demand for insulin. Increased demand for insulin is thought to be related, in part, to a reduced ability of peripheral target cells to bind insulin.

4. The extent and severity of atherosclerosis is increased in patients with longstanding diabetes. As a result, atherosclerotic coronary heart disease is the major cause of death among adults with diabetes.

5. Hyaline arteriolosclerosis and capillary basement membrane thickening are characteristic vascular changes seen in diabetics.

6. Approximately 35% of patients with Type I diabetes will ultimately develop renal failure.

7. Diabetes is a leading cause of blindness. Ten percent (10%) of patients with Type I diabetes of 30 years' duration are legally blind.

8. Peripheral sensory and autonomic nerve dysfunction (peripheral neuropathy) is one of the most common complications of diabetes.

9. Bladder and urinary tract infections are common in diabetes, owning to the elevated levels of sugar in the urine. Pyelonephritis and necrotizing papillitis are devastating complications of renal infection.