Infarction
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In medicine, an infarction is the process of tissue death (necrosis) caused by blockage of the tissue's blood supply. The supplying artery may be blocked by an obstruction (e.g. an embolus, thrombus, or atherosclerotic plaque), may be mechanically compressed (e.g. tumor, volvulus, or hernia), ruptured by trauma (e.g. atherosclerosis or vasculitides), or vasoconstricted (e.g. cocaine vasoconstriction leading to myocardial infarction).
Infarctions are commonly associated with hypertension or atherosclerosis. In atherosclerotic formations a plaque develops under a fibrous cap. When the fibrous cap is degraded by metalloproteinases released from macrophages or by intravascular shear force from blood flow subendothelial thrombogenic material (extracellular matrix) is exposed to circulating platelets and thrombus formation occurs on the vessel wall occluding blood flow. Occasionally, the plaque may rupture forming an embolus that travels with the blood flow downstream where the vessel narrows and eventually clogs the vessel lumen. Infarctions can also involve mechanical blockage of the blood supply, such as when part of the gut or testicles herniates or becomes involved in a volvulus.
[edit] Classification
Infarctions are divided into 2 types according to the amount of blood present:
- White infarctions (anemic infarcts) affect solid organs such as the heart, spleen and kidneys wherein the solidity of the tissue (biology) substantially limits the amount of nutrients (blood/oxygen/glucose/fuel) that can flow into the area of ischemic necrosis. Similar occlusion to blood flow and consequent necrosis can occur as a result of severe vasoconstriction as illustrated in severe Raynaud's phenomenon that can lead to irreversible gangrene.
- Red infarctions (hemorrhagic infarcts), generally affect the lungs or other loose organs (testis, ovary, small intestines). The occlusion consists more of red blood cells and fibrin strands. Characteristics of red infarcts include: occlusion of a vein; loose tissues that allow blood to collect in the infarcted zone; tissues with a dual circulatory system (lung, small intestines); tissues previously congested from sluggish venous outflow; and reperfusion (injury)[1] of previously ischemic tissue that is associated with reperfusion-related diseases[2] such as - Myocardial infarction, stroke (cerebral infarction), shock-resuscitation, replantation surgery, frostbite, burns and organ transplantation.
[edit] Diseases
Diseases commonly associated with infarctions include:
- Myocardial infarction (heart attack)
- Pulmonary embolism ("lung attack")
- Cerebral infarction (stroke)
- Peripheral artery occlusive disease (the most severe form of which is gangrene)
- Antiphospholipid syndrome
- Sepsis
- Giant-cell arteritis (GCA)
- Hernia
- Volvulus
- Splenic infarction
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