How Sugar Is Metabolized - What Is Diabetes: Diabetes
Content provided by the Faculty of the Harvard Medical School
How sugar is metabolized
Many of the cells in your body need sugar as a source of energy. When you eat carbohydrates, such as a bowl of pasta or some vegetables, your digestive system breaks the carbohydrates down into simple sugars (generally glucose), which are ferried into and through your bloodstream to nourish and energize cells.
A key player in the metabolism of sugar is the pancreas, an elongated gland behind your stomach and liver. The pancreas fills two roles. First, it produces enzymes that flow into the small intestine to help your body digest proteins, carbohydrates, and fats. Second, it makes hormones that regulate the disposal of nutrients, including sugars. The islets of Langerhans, tiny clusters of cells found throughout the pancreas, are responsible for producing these hormones. They are composed of alpha cells, which produce the hormone glucagon, and beta cells, which secrete insulin. These hormones generally have opposite actions, but both are important in regulating your body's use of sugar, fat, and protein.
Much like traffic cops dispatched at rush hour to ease congestion, insulin is released by beta cells in response to the rise in blood sugar levels after you've eaten. By directing sugar into liver and muscle cells, it promotes the storage of nutrients and prevents blood sugar levels from rising excessively. It also increases the uptake of amino acids (the building blocks of proteins) and fatty acids (the building blocks of fats) into protein and fat stores, respectively. Insulin thus serves as one of the principal gatekeepers of metabolism, promoting energy storage and growth.
The liver converts glucose that is not needed immediately for energy into glycogen. When blood glucose levels drop too low, your pancreas releases the hormone glucagon, which prompts your liver to reconvert stored glycogen into glucose and release it into the bloodstream. Usually insulin and glucagon levels fluctuate in a coordinated fashion to keep your blood glucose levels within a rather narrow range. This is important because certain organs, such as the brain and kidneys, depend on a consistent, steady supply of glucose. A normally functioning pancreas assures your body of a stable supply of nutrients.
In healthy people, insulin prevents a large rise in blood sugar after eating. The normal blood sugar level before breakfast usually hovers between 70 and 110 milligrams per deciliter (mg/dL). Normal levels of sugar in the blood rarely exceed 180 mg/dL, even after having eaten a meal.
Diabetes mellitus through timeThe first mention of symptoms characteristic of diabetes is found in the Ebers papyrus, which contains medical writings from the ancient Egyptian city of Thebes that date to about 1550 B.C. The Greek physician Aretaeus (200 A.D.) coined the term "diabetes," which in Greek means "siphon" or "pass through," to denote the excessive urination and constant thirst that he observed in his patients. The Latin word mellitus, which means honeyed or sweet, was added centuries later, when medical practitioners realized that the urine of people with diabetes seemed to contain sugar. Documents traced to an Indian physician, Susruta, from 400 B.C., noted that some people produced "honey urine" that attracted flies. Pouring urine onto an anthill to see whether the insects swarmed to it was a crude diagnostic test. Two 19th-century discoveries shed a great deal of light on diabetes. In 1869, while examining pancreatic tissue under a microscope, German medical student Paul Langerhans noticed groups of tiny cells like islands in the midst of a sea. He didn't know it, but these islets of Langerhans, as they are called today, contain the beta cells that produce insulin. In 1889, while exploring how the body metabolizes fat, European scientists Joseph von Mering and Oskar Minkowski found that when they removed the pancreas from a dog, the animal started to urinate uncontrollably. They tested the urine and found that it contained glucose. Recognizing that the dog had developed diabetes, the scientists concluded that the key to the illness resided in the pancreas. |
| Last updated: | January 23, 2007 |
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Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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