How Diabetes Works

The high blood glucose in diabetes produces glucose in the urine and frequent urination through effects on the kidneys.

Insulin Ineffectiveness

Now that you know the symptoms of diabetes -- high blood glucose, excessive hunger and thirst, frequent urination -- let's look at what happens to your body during diabetes. For the purposes of this discussion, let's suppose that you have undiagnosed, and therefore unmanaged, diabetes.

Now, let's see how the lack of insulin or insulin-resistance affects your body to produce the clinical symptoms and signs of diabetes:

Your lack of insulin or insulin resistance directly causes high blood-glucose levels during fasting and after a meal (reduced glucose tolerance).

  1. Because your body either does not produce or does not respond to insulin, your cells do not absorb glucose from your bloodstream, which causes you to have high blood-glucose levels.
  2. Because your cells have no glucose coming into them from your blood, your body "thinks" that it is starving.
  3. Your pancreatic alpha cells secrete glucagon, and glucagon levels in your blood rise.
  4. Glucagon acts on your liver and muscles to breakdown stored glycogen and release glucose into the blood.
  5. Glucagon also act on your liver and kidneys to produce and release glucose by gluconeogenesis.
  6. Both of these actions of glucagon further raise your blood-glucose levels.

High blood glucose causes glucose to appear in your urine.

  1. High blood-glucose levels increase the amount of glucose filtered by your kidneys.
  2. The amount of glucose filtered exceeds the amount that your kidneys can reabsorb.
  3. The excess glucose gets lost into the urine and can be detected by glucose test strips (see How Your Kidneys Work for details on filtration and reabsorption).

High blood glucose causes you to urinate frequently.

  1. High blood glucose increases the amount of glucose filtered by your kidneys.
  2. Because the filtered load of glucose in your kidneys exceeds the amount that they can reabsorb, glucose remains inside the tubule lumen.
  3. The glucose in the tubule retains water, which increases urine flow through the tubule.
  4. The increased urine flow causes you to urinate frequently.
How Diabetes Works

The lack of insulin or insulin resistance acts on many organs to produce a variety of effects.

The high blood glucose and increased urine flow make you constantly thirsty.

  1. High blood-glucose levels increase the osmotic pressure of your blood and directly stimulate the thirst receptors in your brain.
  2. Your increased urine flow causes you to lose body sodium, which also stimulates your thirst receptors.

You are constantly hungry. It's not clear exactly what stimulates your brain's hunger centers, possibly the lack of insulin or high glucagon levels.

  1. You lose weight despite the fact that you are eating more frequently. The lack of insulin or insulin-resistance directly stimulates the breakdown of fats in fat cells and proteins in muscle, leading to weight loss.
  2. Metabolism of fatty acids leads to the production of acidic ketones in the blood (ketoacidosis), which can lead to breathing problems, the smell of acetone on your breath, irregularities in your heart and central-nervous-system depression, which leads to coma.

You feel tired because your cells cannot absorb glucose, leaving them with nothing to burn for energy.

  1. Your hands and feet may feel cold because your high blood-glucose levels cause poor blood circulation.
  2. High blood glucose increases the osmotic pressure of your blood.
  3. The increased osmotic pressure draws water from your tissues, causing them to become dehydrated.
  4. The water in your blood gets lost by the kidneys as urine, which decreases your blood volume.
  5. The decreased blood volume makes your blood thicker (higher concentration of red blood cells), with a consistency like molasses, and more resistant to flow (poor circulation).

Your poor blood circulation causes numbness in your hands and feet, changes in vision, slow-healing wounds and frequent infections. High blood glucose or lack of insulin may also depress the immune system. Ultimately, these can lead to gangrene in the limbs and blindness.

Fortunately, these consequences can be managed by correcting your high blood glucose through diet, exercise and medications, as we'll discuss next.