Editing Embolus (section)

==Classification by substance==
The physical composition of the embolic material is the defining feature for classification, and this composition reflects the underlying pathophysiologic mechanism of the embolus' formation. Furthermore, different types of emboli result in different types of embolisms, each with distinct clinical characteristics.

By contrast, [[embolism]] is typically classified by the location where the emboli lands, such as in [[pulmonary embolism]].

'''[[thromboembolism]]''', the thrombus (blood clot) from a blood vessel is completely or partially detached from the site of thrombosis (clot). The blood flow will then carry the embolus (via blood vessels) to various parts of the body where it can block the lumen (vessel cavity) and cause vessel obstruction or occlusion. The free-moving thrombus is called an embolus.<ref>{{Cite book
 | last1 = Howland
 | first1 = Richard D.
 | last2 = Mycek
 | first2 = Mary J.
 | publication-date =
 | title = Pharmacology
 | edition = 3rd
 | series = Lippincott's illustrated reviews
 | year = 2006
 | publisher = Philadelphia : Lippincott Williams & Wilkins, c2006.
 | page = 227
 | isbn = 0-7817-4118-1
}}</ref> A thrombus is always attached to the vessel wall and is never freely moving in the blood circulation. This is also the key difference for pathologists to determine the cause of a blood clot, either by thrombosis or by post-mortem blood clot. Vessel obstruction will then lead to different pathological issues such as blood [[Stasis (medicine)|stasis]] and [[ischemia]]. However, not only thromboembolism will cause the obstruction of blood flow in vessels, but also any kind of embolism is capable of causing the same problem.

'''[[Fat embolism]]''' usually occurs when endogenous (from sources within the organism) fat tissue escapes into the blood circulation. The usual cause of fat embolism is therefore the [[fracture]] of tubular bones (such as the [[femur]]), which will lead to the leakage of fat tissue within the bone marrow into ruptured vessels. There are also exogenous (from sources of external origin) causes such as intravenous injection of [[emulsions]].

An '''[[air embolism]]''', on the other hand, is usually always caused by exogenic factors. This can be the rupture of [[Pulmonary alveolus|alveoli]], and inhaled air can be leaked into the blood vessels. Other more-common causes include the puncture of the [[subclavian vein]] by accident or during operation where there is negative pressure. Air is then sucked into the veins by the negative pressure caused by thoracic expansion during the inhalation phase of respiration. Air embolism can also happen during intravenous therapy, when air is leaked into the system (however this [[iatrogenic]] error in modern medicine is extremely rare).

'''[[Gas embolism]]''' is a common concern for deep-sea divers because the gases in human blood (usually nitrogen and helium) can be easily dissolved at higher amounts during the descent into deep sea. However, when the diver ascends to the normal atmospheric pressure, the gases become insoluble, causing the formation of small bubbles in the blood. This is also known as [[decompression sickness]] or the bends. This phenomenon is explained by [[Henry's Law]] in physical chemistry.

Embolism by '''other materials''' is rare. [[Septic embolism]] happens when a purulent tissue ([[pus]]-containing tissue) is dislodged from its original focus. [[Tissue embolism]] is analogous to macro-scale [[cancer]] [[metastasis]], which happens when cancer tissue infiltrates blood vessels, and small fragments of tumor are released into the blood stream. [[Foreign-body embolism]] happens when exogenous—and only exogenous—materials such as [[talc]] enter the blood stream and cause occlusion or obstruction of blood circulation.  [[Bullet]] embolism occurs in approximately 0.3% cases of [[gunshot wound]]s.<ref>{{Cite journal|url=http://www.jvascsurg.org/article/S0741-5214%2810%2902639-X/abstract|doi = 10.1016/j.jvs.2010.11.046|title = Retrograde migration and endovascular retrieval of a venous bullet embolus|year = 2011|last1 = Schroeder|first1 = Mary Elizabeth|last2 = Pryor|first2 = Howard I.|last3 = Chun|first3 = Albert K.|last4 = Rahbar|first4 = Rodeen|last5 = Arora|first5 = Subodh|last6 = Vaziri|first6 = Khashayar|journal = Journal of Vascular Surgery|volume = 53|issue = 4|pages = 1113–1115|pmid = 21215588|doi-access = free}}</ref> [[Amniotic-fluid embolism]] is a rare complication of childbirth.