What is Ischemia?
Ischemia is the medical term for an inadequate blood supply to a specific area of the body. This results in a reduced oxygen supply as blood has difficulty in reaching the target tissues or organs. Ischemia can be partial or complete. Partial ischemia may cause hypoxia, which is too little oxygen reaching the area. Complete ischemia results in anoxia, where no oxygen reaches the target area, and if this is not corrected quickly, it will eventually lead to an infarct.
Example : Coronary artery disease results in narrowing of the blood vessels that supply oxygen and nutrients to the heart muscle. Less oxygen is able to reach the heart muscle resulting in ischemia which is sometimes experienced as chest pain, known as angina.
What is Infarct?
Infarct is the when there is death of tissue with surrounding inflammation due to a sudden and complete loss of arterial blood supply. It is often preceded by ischemic injury but if it is gradual and there is only partial ischemia, the body can quickly develop collateral blood supply to the target area. This means that new vessels will branch of from neighboring arteries to carry oxygenated blood to the area. An infarct is a serious medical condition that causes severe disability or even death, depending on the tissue or organ affected.
Example : Total occlusion (blockage) of a coronary artery can result in a myocardial infarct (heart attack) if there is no collateral blood supply to supplement the oxygen provided by the blocked vessel. This leads to an infarct where a portion of the heart muscle dies and the surrounding tissue becomes inflamed.
Ischemia and an infarct can occur in any tissue or organ in the body but is the most life threatening when it affects the heart (heart attack) or brain (cerebrovascular accident or stroke). Although ischemia and infarct are often discussed in the context of a blockage in the artery, like plaques in atherosclerosis or a blood clot (thrombus or embolus), it can also arise from a rupture in the artery thereby preventing oxygenated blood from reaching the target tissue.
What is Necrosis?
Necrosis is the medical term for the death of living cells or tissue. Necrosis occurs due to unnatural factors, as a consequence of external factors. Necrosis should not be confused with apoptosis which is natural cell death.
The exact time of cell death cannot be ascertained, therefore necrosis is technically the structural changes that occur within the cell as a result of death. Necrotic tissue undergoes these changes for a number of reasons – either due to oxygen deprivation, enzymatic dissolution, infection and other forms of trauma to the cell.
Process of Cell Death
Cell death may occur due to a number of reasons. However, the changes that occur from an interrupted oxygen supply to a cell may progress as follows :
- The cell’s mitochondria (energy factories) switch to anaerobic respiration due to the lack of oxygen and lactic acid is produced.
- This lactic acid builds up in the cell and drops the pH (making it acidic) within the cell.
- This acidic environment within the cell triggers the release of enzymes known as lysosomes.
- These lysosomes begin the cellular breakdown.
- The cell membrane cannot maintain its normal function and cellular products escape the cell, while other compounds from the surrounding tissue fluid enters the cell.
- This then permanently damages the mitochondria, rendering them inactive, while any proteins within the cells are denatured.
- The nucleus of the cell then undergoes changes leading to the damage of the DNA and other structures within the nucleus.
- The cytoplasm of the cell becomes flooded and the cell swells.
- The cell membrane ruptures and adjacent cell remnants fuse into a mass.
The enzymes and other substances released from a ruptured cell can also kill healthy cells lying adjacent to it, thereby perpetuating the spread of necrosis. Alternatively it may cause inflammation of the surrounding healthy tissue. A large mass of necrotic tissue is known as gangrene.