What Causes Diabetes?
Diabetes mellitus occurs when the body's cells are unable to obtain or utilize adequate amounts of the hormone insulin. Insulin is secreted by special cells, called beta cells, that are found in certain cell groups, the islets of Langer-hans, in the pancreas. When insulin is present in the bloodstream, it normally enables the body cells to absorb and metabolize (burn) the sugar glucose, a major constituent of carbohydrate foods. In most diabetics, the amount of insulin in the blood is higher than in normal people, but the effectiveness of the hormone is impaired, either by the presence of insulin antagonists or by tissue resistance to the hormone's action.
Furthermore, the release of insulin from the pancreas after eating is delayed in diabetics. Although the body's inability to handle carbohydrates is the major characteristic of diabetes mellitus, the disease may also involve practically every organ of the body without an overt disturbance of glucose metabolism.
Diabetes may occur at any age, but most cases are diagnosed in people between the ages of 40 and 60. Although both sexes are affected by the disease, females are generally more susceptible.
Causes and Characteristics of Diabetes
Insulin is produced in the pancreas by certain cells within cell clusters known as the islets of Langerhans. It is believed that insulin helps transport glucose, a simple sugar normally present in the bloodstream, into body cells, where it is burned for energy. If insufficient quantities of insulin are produced, much of the glucose is not transported to and used by the cells. Instead the glucose remains in the blood and is excreted by the kidneys into the urine.
A deficiency of insulin may occur for several reasons. However, most cases are probably caused by the presence of excessive quantities of substances that either inactivate insulin or in some way block or counteract its effect. Many patients have a family history of diabetes, and the tendency to develop the disorder is probably hereditary.
Diabetes may greatly alter the metabolic activities of the body. Excessive sugar in the urine stimulates the production of large quantities of urine, which leads to dehydration, or drying out, of the body tissues. Because the body cells are unable to use glucose for energy, they tend to burn fat instead and produce excessive quantities of acidic compounds, particularly acetone. The presence of the acidic substances may upset the acid-base balance of the body and produce acidosis, a condition that may lead to coma and death.
Types of Diabetes
There are two basic forms of diabetes mellitus. One form is known as the adult, or mature, form because it usually does not occur before the age of 40. The second form is called juvenile, or youthful, diabetes because it begins early in life. Once they occur, both adult and juvenile diabetes persist throughout the individual's life.
One major difference between juvenile and adult diabetes is that only in the juvenile form is there clear evidence of disease in the pancreas. In people with juvenile diabetes the islets of Langerhans have a marked reduction in the number of beta cells, and the beta cells that are present contain fewer granules than normal cells. These granules are believed to be either insulin itself or its precursor. Because of these changes, the islets produce very little insulin. In patients with adult diabetes, the pancreas may contain the usual number of beta cells and granules, and production of insulin may be normal. In some patients, however, some islets may be replaced by scar tissue or a glassy tissue that is called hyaline.
Another major difference between juvenile and adult diabetes mellitus is that the characteristic symptoms of the disease are much more severe in the juvenile form. In the adult form there may be no symptoms at all.
Besides the juvenile and adult forms of diabetes, there is a condition known as prediabetes or diabetes premellitus. This condition is often associated with the eventual development of overt diabetes. Among the people said to be prediabetic are those who are known to be genetically susceptible- either because an identical twin or both parents have the disease. A woman may also be considered prediabetic if she gives birth to very large babies (over 9 pounds, or 4 kg) or if she has many miscarriages or stillbirths.
Pathology and Symptoms of Diabetes
When carbohydrates are eaten, a hormone secreted from the upper gastrointestinal tract sends out a preliminary call for insulin. From the small intestine, glucose, the major end product of carbohydrate digestion, is absorbed into the blood, bringing about an increase in the sugar content of the blood. This rise in the blood sugar level acts as a stimulus to the beta cells, which then secrete large amounts of insulin into the blood. Although the exact mechanism by which insulin affects the cells is not clearly understood, it apparently facilitates the intake of glucose into each body cell where it is metabolized to form large quantities of adenosine triphosphate (ATP), the cell's major source of energy. In liver and muscle cells, insulin also aids in the conversion of glucose into a storage form, called glycogen, and in the liver, insulin is also required for the conversion of glucose into fat.
In people with diabetes mellitus, the deficiency or unavailability of insulin prevents much of the glucose from entering the body cells, and the glucose accumulates in the blood. Upon reaching a certain level, some of the excess glucose is excreted by the kidneys in the urine. When large amounts of sugar are thus excreted, the patient produces larger quantities of urine and has to urinate frequently. In addition, he develops a great thirst, complains of a dry mouth, becomes weaker, and loses weight. In females, the presence of excess sugar in the urine sometimes encourages the growth of fungi in the genital area, producing intense inflammation and itching. Sometimes, the excess sugar in the blood also enters the eye fluids and produces blurring of vision.
When the body cannot metabolize enough glucose to meet its energy needs, fatty acids are released from fat deposits in the body, and they are broken down into smaller units to provide energy. Because of the overproduction of these units, excessive amounts of substances known as ketone bodies are produced. As these substances accumulate in die blood, their acidity produces a condition known as acidosis. The patient becomes markedly dehydrated, is usually vomiting, and has deep labored breathing. If the patient's condition is not alleviated, he sinks into diabetic coma and may die.
Because diabetes does not usually produce symptoms, the condition is often first discovered by a physician during a routine physical examination, when he detects sugar in the urine. Since other conditions may occasionally cause sugar to appear in the urine, the physician confirms the diagnosis by measuring the amount of sugar in the blood. In severe cases of diabetes the person may also have acetone in the urine and in the blood, as well as increased acidity of the blood.
Treatment of Diabetes
There is no known cure for diabetes, and all therapeutic measures are aimed at limiting the disease and relieving die patient's symptoms. Of chief importance in die control of diabetes mellitus are a proper diet, sufficient exercise, and die administration of drugs to reduce the blood sugar level. Sometimes only a slight restriction of carbohydrates is all that is necessary. In other cases, a very strict curtailment in the diet is required. In general, all diabetics should avoid candy, cake, jam, and ice cream. Other carbohydrate-rich foods, such as bread, cereal, fruits, and certain vegetables, should be limited. A common error made by diabetics is the drinking of canned fruit juices to which no sugar has been added. The patient often forgets that fruit juices contain natural sugar. Sugar-free hard candies and chewing gum are permissible, as are sugarless carbonated beverages. Alcohol in moderate quantities is very useful to elderly people and should not be forbidden.
The adult form of diabetes often requires die administration of oral drugs that stimulate die beta cells to produce more insulin. These drugs are known collectively as sulfonylureas. In juvenile diabetes they are of very little value, and even in adult diabetes they are not always successful, especially if the patient neglects his diet. Sometimes, these drugs work for only one or two years. DBI is a useful drug often used to supplement the sulfonylureas.
The most powerful and reliable antidiabetic agent known is insulin itself. A major drawback of insulin, however, is that it can be administered only by injection, a problem for many blind and other handicapped persons. Commercial preparations of insulin are made in two forms: a clear, quick-acting form and a cloudy suspension that has a delayed, although prolonged action. When insulin is used in treating diabetes, it is important that meals be eaten on time. If a meal is delayed and there is not enough glucose in the bloodstream, the patient may suffer severe reactions, including trembling, cold sweats, hunger, dizziness, and bizarre behavior. These reactions may be corrected by drinking a sweet beverage.
Exercise, such as swimming or walking briskly, is almost as good as a shot of insulin and is very useful in controlling diabetes. When a person exercises, the increased muscle activity allows additional amounts of glucose to be metabolized. Thus, if a diabetic is about to exercise strenuously, he must either reduce his insulin intake or eat more carbohydrates.
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