METABOLIC DISTURBANCES AND COMPLICATIONS OF THE DIABETIC STATE
There are only two major sources of blood glucose: ex-ogenous, or the ingestion of dietary carbohydrate, and endogenous, which is contributed by hepatic and renal gluconeogenesis and hepatic glycogenolysis. Diabetes mellitus is a metabolic disorder in which carbohydrate metabolism is reduced while that of proteins and lipids is increased. In diabetics, exogenous and endogenous glu-cose is not used effectively, and it accumulates in the blood (hyperglycemia). As blood glucose levels in-crease, the amount of glucose filtered by the glomeruli eventually exceeds the reabsorption capacity (Tm, trans-port maximum) of the proximal tubule cells, and glu-cose appears in the urine (glucosuria). Protein catabo-lism and the rate of nitrogen excretion are increased when blood insulin falls to low levels; stimulation of he-patic gluconeogenesis converts amino acids to glucose. The catabolism of lipids and fatty acids is also acceler-ated in the absence of insulin, leading to the formation of ketone bodies, such as acetoacetic acid, -hydroxybu-tyric acid, and acetone. Renal losses of glucose, nitroge-nous substances, and ketone bodies promote osmotic diuresis that can result in dehydration, electrolyte ab-normalities, and acid–base disturbances. Diabetic ke-toacidosis is the end result of insulin deficiency in un-controlled type I diabetes.
Type II diabetics are less prone to develop ketone bodies or diabetic ketoacidosis but may develop hyper-osmolar coma, a condition characterized by severe hy-perglycemia and dehydration. Both diabetic ketoacido-sis and hyperosmolar coma are medical emergencies that require prompt insulin administration and intra-venous fluids.
Diabetes mellitus is associated with many complica-tions that are increased in the setting of poor glycemic control. Diabetes mellitus can cause microvascular complications (e.g., retinopathy, nephropathy, and neu-ropathy) and macrovascular complications (e.g., athero-sclerotic cardiovascular disease), associated with dia-betic dyslipidemia (usually elevated triglycerides and low-density lipoprotein cholesterol). Recent clinical tri-als have demonstrated that the risk of developing chronic complications of diabetes is reduced by achiev-ing good glycemic control. This can be accomplished by a combination of diet, exercise, and rational pharmaco-logical therapy directly targeted to optimize diabetes management.