An anastomosis (plural anastomoses, from gr. ἀναστόμωσις, communicating opening) is a network of streams that both branch out and reconnect, such as blood vessels or leaf veins. The term is used in medicine, biology, and geology.

Medicine

Anastomosis is the connection of two structures. It refers to connections between blood vessels or between other tubular structures such as loops of intestine. In circulatory anastomosis, many arteries naturally anastomose with each other, for example the inferior epigastric artery and superior epigastric artery. An example of Surgical anastomosis occurs when a segment of intestine is resected and the two remaining ends are sewn or stapled together (anastomosed), for example Roux-en-Y anastomosis. The procedure is referred to as intestinal anastomosis.

Pathological anastomosis results from trauma or disease and may involve veins, arteries, or intestines. These are usually referred to as fistulas. In the cases of veins or arteries, traumatic fistulas usually occur between artery and vein. Traumatic intestinal fistulas usually occur between two loops of intestine (enetero-enteric fistula) or intestine and skin (enterocutaneous fistula). Portacaval anastomosis, by contrast, is an anastomosis between a vein of the portal circulation and a vein of the systemic circulation, which allows blood to bypass the liver in patients with portal hypertension, often resulting in hemorrhoids, esophageal varices, or caput medusae.

Biology

In evolution, anastomosis is a recombination of evolutionary lineage. Conventional accounts of evolutionary lineage present themselves as the simple branching out of species into novel forms. Under anastomosis, species might recombine after initial branching out, such as in the case of recent research which shows that ancestral populations along human and chimpanzee lineages may have interbred after an initial branching event. The concept of anastomosis also applies to the theory of symbiogenesis, in which new species emerge from the formation of novel symbiotic relationships.

Geology

In geology, anastomosis refers to quartz (or other) veins displaying this property, which is often related to shearing in metamorphic regions.

There is also a type of stream or river called anastomosing, which consists of a wide strath and multiple thalwegs divided by vegetated stabilized islands within subparallel banks.

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