Over the course of our lives our bodies experience “wear and tear” just like an engine. For example the smooth cartilage in our joints wears off over time and then we experience pain and inflammation in this joint, also called “arthrosis” and “arthritis”. The elasticity of the skin diminishes and it wrinkles. The lens in our eyes stiffens and we need reading glasses. There are countless examples and we have more or less accepted this as fact of life. However besides time and aging there are conditions or diseases that also cause “wear and tear” on our body. For example a higher than normal glucose level in our blood stream damages the lining of our arteries and veins. That extra “stress” is only tolerated for so long and then damage manifests itself. Eventually vessels constrict or close up. The same applies for high lipid levels and high pressure in our blood stream. Ultimately blood supply is not sufficient in all places.
When blood supply to an organ is impaired because of injured blood vessels the organ’s function will suffer. Most of the times this happens gradually, take the heart for example, first you have chest pain during exercise (chest pain being the symptom of the heart not getting enough blood supply), then just with little physical exertion and then even during rest. When no intervention follows a heart attack will be next. During all this time improvement of blood supply would result in return to mostly normal performance level of the heart. After a heart attack has happened the organ is permanently damaged and return to normal is not possible. Depending on the size of damage, pumping capacity is decreased. When the damage is too big to compensate for you die. This is one example of “target organ damage”. Others would be a stroke in the brain, chronic kidney failure, loss of a limb etc.