Ischemia represents oxygen deficiency in tissues occurring due to narrowing or blockage of a blood vessel. Hence it can be in a relative narrowing of the vascular lumen or absolute – in its complete blockage. There are two reasons that could lead to ischemia:
1. Obstruction or stenosis of the vascular lumen – the reason is a change in the vascular wall – atherosclerotic plaques.
2. Functional vascular stenosis – due to spasm of smooth muscle in the vessel wall.
Ischemia results in tissue damage, because they do not supply enough nutrients and oxygen. Simultaneously retention becomes degraded substances – metabolites of intermediate metabolism in the ischemic area. Ischemia can have different effects depending on whether it is complete obstruction of a particular vessel, its duration, sensitivity to oxygen starvation of the affected tissue and the presence of anastomoses court with surrounding vascular branches. Arteries that no anastomoses are referred to as terminal. Some of them have no anastomoses, others have capillary anastomoses that are able to provide oxygen to the ischemic area. They are called functional end arteries.
Relative ischemia is one where there is an imbalance between blood supply and tissue need thereof. Morphological change of the tissue at the relative ischemia are usually mild and are presented by swelling of mitochondria, but in single or group of cells can be monitored coagulation necrosis. An example of such a condition is called intermittent claudication, which affects elderly people with atherosclerotic changes in the blood vessels of the lower limbs.
Chronic relative ischemia as a result of functional end-arteries or arterioles leading to atrophy, degeneration and scarring of the affected tissues. Such an example may be the focal miocardiofyndosis in chronic ischemic heart disease, determined by coronarosclerosis.