Diabetes can be a very confusing disease to understand. I will break it down into small, easy to understand chunks.
Diabetes is a disease whereby the body has trouble 'dealing with' sugar. Sometimes 'sugar' is used interchangeably with 'carbohydrate.' A carbohydrate is a nutritional macromolecule that encompasses all the many different forms that sugar can take: glucose, fructose, lactose, and sucrose are examples
Carbohydrates are everywhere - in most of the foods we eat. Obviously there is sugar (therefore carbohydrates) in sodas and candy, but there's also carbohydrates in fruit, pasta, and bread. And the thing is, your body sees all sugar, and all carbohydrates the same. It 'deals with' carbohydrates the same, no matter the source (whether from a candy bar, or a piece of wheat toast).
In normal, non-diabetic people, when you eat something that contains sugar (even a vegetable that has carbohydrate/sugars), a cascade of events are initiated.
After you ingest sugar, the sugar level in your blood stream rises. Your body DOES NOT like the blood sugar level to be too high. The normal range is 80-140 mg/dL. So, insulin is released when sugar levels rise. Insulin is a hormone who's job is to lower the blood sugar level by causing the cells of the liver, muscle, and fat to suck up the sugar from the blood. The cells then convert the sugar into it's storage forms, either fat, or glycogen, for later use.
In diabetic people, the sugar is not 'handled' properly by their bodies, and this causes both short term, and long-term complications.
There are 2 main types of diabetes commonly discussed, Type I, and Type II. Although they both manifest with problems in blood sugar control, they are opposite diseases.
Type 1 Diabetes:
Type 1 Diabetes is a disease where there isn't any insulin being made by your pancreas.
The cause is probably an auto-immune destruction of the insulin producing cells in the pancreas (but there are other theories as well). Without insulin, the sugar that you eat stays in your blood stream and cannot be lowered by the usual mechanism of shifting it inside of cells (which is used for energy and storage).
Mechanism of disease: As I mentioned, your body does not like too much sugar floating around in your blood stream. And in the Type 1 diabetics, the sugar can get very high. The reason for this to two-fold. First, the sugar that's eaten cannot be taken up by the liver, muscle, and fat cells. Second, there is another hormone (that has the opposite/balancing effect of insulin) called glucagon, and if insulin is not present, the glucagon works unopposed (alone) and causes a rise in blood sugar.
This elevated blood sugar causes an 'osmotic diuresis' which means that the sugar that your kidneys are trying to excrete (to help lower your body's load) is pulling lots of water, sodium and potassium with it (because that's how chemistry works). So, you get very dehydrated very quickly, and your electrolytes become deranged (very abnormal).
In addition to the high sugar, and dehydration, another problem develops. See, your body needs energy to continue to do the things it need to do (like breathe, digest food, walk, think, maintain your heart beating). This energy comes from the foods you eat. If your body is unable to utilize the food (insulin is needed to get the sugar into the cells, if there is no insulin, the cells have no way to use energy) it starts to use it's body stores of energy to stay alive. This means breaking down muscle protein, and using fat (fatty acids) as an energy source. The problem with this is, it goes on and on. And the by-products of fatty acid breakdown (ketone bodies) start to increase. These ketone bodies are acidic. So the blood becomes more acidic as more of the ketone bodies are being produced. This is a diabetic emergency called DKA (diabetic ketoacidosis).
The good news is even a little bit of insulin in your body helps prevent this whole cycle from spinning out of control. When the ketone body concentration gets too high, a normal pancreas will release a small amount of insulin to stop ketone production. Type 1 diabetics have to rely on insulin injections to stop ketone production.
Symptoms of Type I diabetes typically include excessive thirst, excessive urination, weight loss despite eating lots of food, and lack of energy.
Type I Diabetes is diagnosed by checking your blood sugar level fasting (after not eating for a period of time). If that level is greater than 126 mg/dl, you have diabetes. OR if your blood sugar level is greater than 200 mg/dL two hours after drinking a 75g glucose load, such as a special soda (this is called a glucose tolerance test, and is commonly done in pregnancy). OR if you have a blood sugar greater than 200 mg/dL and have symptoms of diabetes.
The treatment for Type I DM is insulin supplementation for life. This can be done with daily injections, or with insulin pumps. There are some cases of pancreas (or islet cell) transplant
Prognosis: You cannot survive without any insulin. So, without treatment, Type I diabetes is a fatal disease.
Type 2 Diabetes
Type 2 Diabetes is more common, and typically develops later in life (although with our obesity epidemic, many young children are actually developing type 2 diabetes early).
Type 2 diabetes is a disease of *insulin resistance*. There is PLENTY of insulin around, but your body simply cannot use it. See, what happens is, as you eat more and more carbohydrates/sugars, your pancreas has to work overtime squirting out insulin to get your blood sugar down into a normal range. After awhile two things happen: 1) your pancreas just gets tired and is unable to keep up with the demand. 2) your body (specifically the body cells that respond to insulin such as the muscle, liver, and fat cells) become 'numb' to insulin. They don't respond to normal doses. They become RESISTANT to insulin.
Insulin resistance is a HUGE problem in our society.
The symptoms of type 2 diabetes are very similar to type I. However, with type I DM, because there is NO insulin, the blood sugar rises rapidly and ketone bodies cause a life-threatening acidosis. In type 2, there is insulin around, so the ketone body formation is not as significant (so DKA is uncommon). Because it is the ketone bodies that make you very sick with diabetes in the short-term, people with type 2 diabetes may go months or years without knowing they have diabetes (because they don't feel very sick).
The long term complications of diabetes results from chronically elevated blood sugar levels. Our bodies do not like the sugar to be too high. High blood sugars cause damage to the nerves (neuropathy), kidney failure (nephropathy), erectile dysfunction, blindness, slow healing wounds, vascular disease (including strokes and heart attacks), and increases the likelihood of infections. Neuropathy can cause problems with your digestive system (diabetic gastroparesis) which is a very painful condition where the intestine does not push the food through normally resulting in abdominal pain, nausea and vomiting that can lead to further dehydration and hospitalization.
Type 2 diabetes is diagnosed the same as Type I, but usually at a routine physical rather than as an emergency.
Prognosis is better with type 2 DM because there IS some insulin present (even if the pancreas is tired and burnt-out, there's still usually some insulin still being produced) and that small amount of insulin can (usually) prevent the more immediately fatal complication of DKA.