Complications due to diabetes can be usually traced to either damage to nerves, blood vessels, or a combination of the two. Damage to blood vessels is usually categorized by the size of the blood vessels. Doctors talk about damage to large blood vessels as macrovascular disease, while damage to small blood vessels is called microvascular disease.
Nerve damage, or neuropathy, is one of the primary complications of diabetes. Neuropathy can manifest itself in many different forms, leading to many different symptoms. We already saw that peripheral neuropathy leads to problems with the feet. Diabetic patients can also suffer damage in autonomic nerves, those that control the parts of the body you never think about. For instance, damage to the nerves that control the digestive system lead to symptoms like urinary tract infections, diarrhea, constipation, or vomiting. Damage to the nerves that controls the heart can lead to reduced heart rate variability; then vigorous exercise might not be accompanied by an appropriate increase in heart rate.
Macrovascular disease takes the form of atherosclerosis, which is where plaque builds up inside the arteries. The plaque can cause two types of problems: it slowly narrows the arteries, restricting the flow of blood and, sometimes, a piece of the plaque can break off producing a sudden acute blockage, a thrombosis. If the gradual narrowing of the arteries occurs in the coronary arteries, you can get angina, or chest pain. If the gradual narrowing occurs on the arteries that feed the kidney, you can get chronic kidney disease, leading to kidney failure. If the thrombosis blocks blood in the brain, you can have a stroke. If it blocks blood in a coronary artery, you have a heart attack.
Microvascular disease occurs in the capillaries, the tiny blood vessels connecting the arteries to the veins. Blood cells can stick together in these tiny vessels causing a micro-blockage. Since the vessels are so small, blood leaks out of the vessel into the surrounding tissue. Depending on where in the body this occurs, you can have very different effects. Microvascular disease that occurs in the retina of the eye, diabetic retinopathy, is the leading cause of blindness in the United States. Microvascular disease that occurs in the kidneys leads to kidney failure and requires dialysis.