Insulin
Insulin
Insulin is a hormone secreted by the pancreas gland, one of the glands in the endocrine system. Insulin, working in harmony with other hormones, regulates the level of blood sugar (glucose). Endocrine glands are ductless glands; that is, they pour their products (hormones) directly into the bloodstream. The pancreas, a gland in the upper abdomen, has cells within it that secrete insulin directly into the bloodstream. An insufficient level of insulin secretion leads to high blood sugar, a disease called diabetes mellitus or, simply, diabetes. Specifically, diabetes is a metabolic disease caused by the body’s inability to use the hormone insulin to effectively convert carbohydrates into the simple sugar glucose that cells store and use to perform vital functions.
Without glucose to fuel their activity, the cells use fat instead, producing ketones as a waste product. Ketones build up in blood and disrupt brain functions. Common signs of diabetes are excessive thirst, urination, and fatigue. The disease can also cause vision loss, decreased blood supply to hands and feet, pain, and skin infections. If left untreated diabetes can induce coma and cause death. Diabetes often runs in families. In the United States about 10% of the Caucasian population suffers from diabetes, and it is even more common among African-American, Mexican-American, and certain Native American groups. The sixth leading cause of death in the United States, diabetes remains a major health problem. According to the American Diabetes Association, about 20.8 million children and adults (about 7% of the U.S. population), as of 2006, suffer from diabetes mellitus. About 14.6 million people have been diagnosed with diabetes. However, about 6.2 million people (about one-third) do not know that they have diabetes.
History
Prior to the twentieth century, diabetes was a fatal disease. Its cause was unknown, and the method of treating it had yet to be discovered. Not until 1921 did the research of Sir Frederick Grant Banting (1891–1941), a Canadian surgeon and medical scientist, and Charles Herbert Best (1899–1978), a Canadian physiologist and medical scientist, reveal that insulin is crucial in blood glucose regulation. The two scientists then isolated insulin, an achievement for which they were awarded the Nobel Prize. Their work was built on previous research by Paul Langerhans (1847–1888), a German pathologist and biologist who described the irregular, microscopic collections of cells scattered throughout the pancreas. These cells later were named the islets of Langerhans and were found to be the source of insulin secretion.
In 1952, British biochemist Frederick Sanger (1918–) analyzed insulin and discovered it was made up of two chains of amino acids. One chain, called the alpha chain, has 21 amino acids and the second chain, the beta chain, has 30 amino acids. The chains run parallel to each other and are connected by disulfide bonds (made up of two sulfuratoms). With the discovery of the chemical structure of insulin, efforts to synthesize it began.
Types of diabetes
Diabetes manifests in two types. Type I diabetes is also called childhood onset because it begins in early childhood. Adult onset diabetes or Type II affects adults.
Glucose is a source of energy to the muscles of the body. Normally, the glucose content of blood is determined by the demands made by the muscles; the secretion of insulin, which lowers blood glucose; the secretion of glucagon, also manufactured and secreted in the pancreas, which raises blood glucose; extraction by the liver of glucose from the blood to be converted to glycogen and stored; and other hormones secreted by the adrenal and pituitary glands. The secretion of glucagon in the pancreas is a function of the alpha cells of the islets of Langerhans, and the secretion of insulin is the function of the beta cells of the same islets.
If the beta cells fail to function properly or are genetically insufficient in number to provide the needed hormone, diabetes can result. Also, in adults, the damage to, or failure of the cells resulting in lowered insulin secretion can lead to diabetes mellitus.
No cure has been found for diabetes; that is, no way has been found to restore full function to the beta cells in the islets of Langerhans. Individuals who have diabetes must take insulin by injection or take pills that control carbohydratemetabolism.
The insulin used by diabetics used to be extracted from porcine (pig) and bovine (cattle) pancreas. However, with the genetic revolution, genetic engineering has allowed bacteria to be transformed to produce human insulin protein, which is purified from large industrial cultures. Thus, human insulin is obtained from bacteria that have human genes inserted into them. Human insulin technology has advanced to produce new, more effective forms of insulin. One of the problems with insulin therapy is that diabetic patients must inject themselves with insulin regularly– an unpleasant process for many people. The development of Humulin-L, Humulin-N, Humulin-R, and Humulin-U have allowed some patients to reduce the frequency of shots required. These new forms of human insulin (from which the name Humulin comes) have effects that last longer than ordinary insulin, making fewer injections possible. As a result, more diabetes patients are likely to stick to their insulin therapy.