Insulin and Diabetes
Today we know that diabetes is caused by the inability to produce or properly respond to insulin. There are two main types of the condition. Type 1 diabetes, which represents about 5% of all adult cases, is due to pathological destruction of the insulin-producing cells in the islets of Langerhans. People with type 1 diabetes require daily injections of insulin to survive. Type 2 diabetes, which accounts for about 90%–95% of all adult cases, begins when cells in the body don’t respond to insulin; researchers don’t fully understand why this happens. Having cells that are unresponsive to insulin is as bad as not making insulin at all.
Normally, insulin binds to receptors on target cells and triggers the cells to take up glucose from blood. This glucose is then used by the cells as a source of energy. Without properly functioning insulin (or insulin receptors), cells cannot take up sugar from the blood and so they starve (INFOGRAPHIC M7.3).
The pancreas produces other hormones as well, including glucagon, which raises blood sugar. The two hormones work together to regulate blood sugar through a classic negative feedback loop. (For more on glucose metabolism, including the role of glucagon, see Chapter 25.)
Left untreated, chronic diabetes can cause a suite of health problems: increased risk of heart disease and stroke, loss of vision, kidney disease, nerve damage–and, eventually, death. An estimated 26 million Americans (roughly 8% of the population) suffer from diabetes, making it the most common endocrine disorder in the United States.
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