The Joslin Guide to Diabetes: A Program for Managing Your Treatment

First Chapter

Chapter 1

What Is Diabetes?

Anytime you want to learn about a medical problem, it's best to approach it in two steps. First, learn how the body functions normally. Then focus on what happens when something goes wrong. This is the best way to learn about diabetes, too. First, you need to understand how the body normally produces energy. You should then focus on how a breakdown in this process leads to the two major types of diabetes -- either your body can't make any or enough insulin, or it can't properly use the insulin it produces.

How the Body Normally Produces Energy

Quite simply, you can't live without food. The body needs food to nourish itself and sustain life. Food is both "fuel" and "building material." It produces energy, builds and repairs body tissue, and regulates body functions. But before food is used by the cells, it's put through some biological paces. First, your body must break down the food you eat into its basic ingredients, or nutrients: These nutrients fall into three major categories -- carbohydrates, proteins, and fats.

Carbohydrates are found in most foods. Often called "starches" and "sugars," they are found in bread, pasta, fruits, and vegetables. Proteins are found in meats, milk, and fish. Fats are found in such foods as vegetable oils, meat, cheese, and other dairy products. All these nutrients are digested, or broken down, in the stomach and intestines. Carbohydrates are broken down into a simple sugar called glucose, which passes through the wall of the intestines into your bloodstream. This is the form of sugar that is often called "blood glucose" or, more simply,just "blood sugar." Diabetes is a disorder in the way the body uses blood sugar, or glucose.

The Role of Insulin

Once glucose gets into your bloodstream, it circulates to the body's cells to provide them energy. But glucose can't simply flow into the cells. All cells are enclosed by a thin wall called a membrane, and something has to tell your cells that glucose is waiting outside. That something is insulin. It attaches on the outside of the cells to special sites called insulin receptors -- much like a key that fits into a lock. Insulin is the "key" that unlocks the cells, allowing glucose to enter. Once inside, the glucose is metabolized, or "burned," by the cells for energy.

Exactly what kind of substance is insulin? It is a hormone -- a chemical messenger made in one part of the body to transmit "information" through your bloodstream to cells in another part of the body. Your body produces many types of hormones. Insulin is a specific kind of hormone made in the organ called the pancreas.

The Pancreas

The pancreas is a small gland situated below and behind the stomach. In an adult, it weighs less than half a pound. The pancreas is shaped like a long cone lying on its side, with the end tapering off into a "tail." Within this tail are tiny bits of tissue called islets of Langerhans.

A normal pancreas has about 100,000 islets of Langerhans. But these islets are actually clusters of various types of cells. The most important are the beta cells -- the tiny "factories" that make insulin. The beta cells also serve as "warehouses," storing insulin until it's needed by the body.

In addition to producing insulin, the pancreas has other important duties. Some cells produce hormones that are quite different from insulin, such as glucagon. This hormone actually raises the blood sugar -- just the opposite function of insulin. The balancing act between insulin and glucagon helps keep blood sugar in the normal range, approximately 60-140 milligrams (mg) of sugar per deciliter (dl) of blood. Other cells in the pancreas produce substances called enzymes, which help in digestion by splitting foodstuffs into simpler substances, which can then be absorbed through the intestine into the bloodstream.

How Insulin Works

During normal digestion, enzymes in the stomach and intestines act upon the nutrients (carbohydrates, proteins, and fats), splitting them into simple substances, which enter the bloodstream in the following forms:

* Carbohydrates are converted into glucose, which is metabolized, or "burned," for energy.
* Proteins are converted into amino acids, which provide the basic building blocks for bone, muscle, and other tissues. Proteins also can be burned for energy.
* Fats become fatty acids, which are burned for energy or stored as body fat for later use. However, fat is burned differently from glucose, producing substances called ketones.

Insulin plays a role in the burning and storage of all these nutrients. In diabetes, however, its main role relates to the action of glucose, the simplified form of carbohydrates. The whole process works like a dietary drama. The key actors are the beta cells, which make and store insulin. When they sense the level of glucose rising in the blood, they respond by releasing just the right amount of insulin into the bloodstream.

At first, the beta cells release the insulin held in storage. But what if the body needs even more? This often happens right after a meal, and as the blood glucose levels increase, a second stage begins. The "control centers" of the beta cells trigger them to make more insulin. When functioning normally, the beta cells release just enough insulin to maintain the level of glucose in the blood within the normal range of 60-140 mg/dl, and once in the bloodstream, the insulin enables the glucose to enter your body's cells for energy.

Another process also occurs. Generally when you eat, you don't need to use all the glucose from your food immediately. The body takes some of the glucose and stores it for future needs. With insulin's help, the extra glucose is taken up by the liver cells and changed to a storage form called glycogen. Glycogen comes in handy when your body needs extra energy in a hurry, for instance, during exercise. At those times, your body rises to the occasion by quickly changing the stored glycogen back into glucose. In addition, this stored glucose takes care of your energy needs overnight, a time when you normally aren't eating. Insulin also helps convert some of the extra glucose into fat, which is stored in the body's fat cells.

What Goes Wrong in Diabetes?

Diabetes is caused by a breakdown in the normal processes described above. A breakdown can occur in one of two ways: (1) the body produces little or no insulin; or (2) the insulin that the body produces can't link up with the body's cells. Type I diabetes is the result of the first defect; Type II is the result of the second. It is important to note, however, that there are many similarities between Type I and Type II diabetes, and that some people display characteristics of both types.

Type I: Insulin-Dependent Diabetes

Of all people with diabetes, about 5-10 percent have Type I, which develops most often in children and young adults. That's why it was once called "juvenile-onset" diabetes. However, this type of diabetes can occur in people of any age.

The Problem. Type I diabetes occurs when the pancreas produces very little, if any, insulin. In short, the beta cells do not function. People with this type of diabetes are insulin-dependent. They must have daily doses of insulin from an outside source to function and survive. Insulin must be provided by injection with a syringe ("a shot"). It cannot be taken by mouth because the stomach acids make insulin ineffective.

The Symptoms. By understanding what happens when the body lacks insulin, you can understand the various symptoms of diabetes -- the outward signs that something is wrong.