Diabetes

Glucose Metabolism

DM is caused by an inability of the pancreas to produce the hormone insulin in a sufficient quantity to meet the body's demands. The pancreas is an exocrine and endocrine organ located behind the stomach in the abdomen. It secretes certain important digestive enzymes into the small intestine to break down food (exocrine function), but it also secretes hormones such as insulin, glucagon, and somatostatin into the bloodstream to regulate the body's nutrient use (endocrine function). The β-cells of the pancreas secrete insulin in response to eating. This hormone acts at receptors in the liver, muscles, and other organs to allow their uptake of glucose, the simple sugar carbohydrate that is the body's primary energy source. The tissues of the body use the energy from glucose to perform their normal physiologic functions. If there is an excess of glucose, the liver and muscles can store it for later use as glycogen, a more complex carbohydrate consisting of chains of glucose. Insulin also allows the body to turn free fatty acids (FFA) into triglycerides, the main component of adipose (fat) tissue. Without insulin, the body cannot use the glucose in the bloodstream, despite its abundance after a meal. To compensate, tissues break down protein and fats for energy, a situation similar to starvation. DM results either when the pancreas does not produce enough insulin or when the body becomes resistant to the effects of insulin. Regardless, the common outcome is hyperglycemia (elevated blood glucose levels) and a paradoxical inability of the body's tissues to use this glucose.

Definition of DM

The term diabetes most commonly refers to the endocrine disorders of carbohydrate metabolism known as diabetes mellitus (DM), conditions characterized by hyperglycemia. Originating from the Greek for “one that straddles” or “a siphon,” the word diabetes alone, however, also encompasses a number of metabolic disturbances that result in increased urine production, including DM and diabetes insipidus (DI). Unlike DM, DI is a condition of increased urine output that is not caused by increased glucose levels. It is categorized by etiology. Nephrogenic diabetes insipidus (NDI) is due to an inability of the kidney to concentrate urine and can be caused by a genetic mutation or by treatment with the mood stabilizer lithium. Central diabetes insipidus (CDI) is generally caused by an inability of the central nervous system to detect and regulate the electrolyte concentration of the body's fluids; it can be caused by head trauma and some cancers. DI represents a distinct pathophysiologic process from DM and is not associated with the numerous complications of the latter.

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