The endocrine pancreas consists of the islets of Langerhans, which contain four major cell types—beta, alpha, delta, and PP (pancreatic polypeptide) cells. The beta cell produces insulin, which regulates glucose utilization in tissues and reduces blood glucose levels, as will be detailed in the discussion of diabetes; the alpha cell secretes glucagon, which raises glucose levels through its glycogenolytic activity in the liver; delta cells secrete somatostatin, which suppresses both insulin and glucagon release; and PP cells secrete pancreatic polypeptide, which exerts several gastrointestinal effects, such as stimulation of secretion of gastric and intestinal enzymes and inhibition of intestinal motility. The most important disease of the endocrine pancreas is diabetes mellitus, caused by deficient production or action of insulin.
Diabetes mellitus is a group of metabolic disorders characterized by hyperglycemia. Hyperglycemia in diabetes (in common parlance, the suffix “mellitus” is often not used) results from defects in insulin secretion, insulin action, or, most commonly, both. The chronic hyperglycemia and attendant metabolic abnormalities of diabetes are often associated with secondary damage in multiple organ systems, especially the kidneys, eyes, nerves, and blood vessels. In the United States, diabetes is the leading cause of end-stage renal disease, adult-onset blindness, and nontraumatic lower-extremity amputations resulting from atherosclerosis of arteries.
According to the American Diabetes Association, diabetes affects over 29 million children and adults, or 9.3% of the population, in the United States, nearly one-third of whom are currently unaware that they have hyperglycemia. Approximately 1.4 million new cases of diabetes are diagnosed each year in the United States, and there is a wide variability in prevalence between different ethnic groups. For example, the prevalence of diabetes in American Indian/Alaskan Natives is almost twice that of Caucasians. Increasingly sedentary lifestyles and poor eating habits have contributed to the increases in diabetes and obesity, which some have termed the diabesity epidemic. A staggering 86 million adults in the United States have prediabetes, which is defined as elevated blood sugar that does not reach the criterion accepted for an outright diagnosis of diabetes (discussed next); individuals with prediabetes have an elevated risk for development of frank diabetes.
Blood glucose is normally maintained in a very narrow range, usually 70 to 120 mg/dL. According to the American Diabetes Association (ADA) and the World Health Organization (WHO), diagnostic criteria for diabetes include the following: 1.
A fasting plasma glucose greater than or equal to 126 mg/dL, and/or 2.
A random plasma glucose greater than or equal to 200 mg/dL (in a patient with classic hyperglycemic signs, discussed later), and/or 3.
A 2-hour plasma glucose greater than or equal to 200 mg/dL during an oral glucose tolerance test with a loading dose of 75 gm, and/or 4.
A glycated hemoglobin (HbA1C) level greater than or equal to 6.5% (glycated hemoglobin is further discussed under chronic complications of diabetes)
All tests, except the random blood glucose test in a patient with classic hyperglycemic signs, need to be repeated and confirmed on a separate day. Of note, many acute conditions associated with stress, such as severe infections, burns, or trauma, can lead to transient hyperglycemia due to secretion of hormones such as catecholamines and cortisol that oppose the effects of insulin. The diagnosis of diabetes requires persistence of hyperglycemia following resolution of the acute illness.