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The circle of Willis (also called Willis' circle, loop of Willis, cerebral arterial circle, and Willis polygon) is a circulatory anastomosis that supplies blood to the brain and surrounding structures in reptiles, birds and mammals, including humans. [1] It is named after Thomas Willis (1621–1675), an English physician. [2]
There are many examples of normal arterio-arterial anastomoses in the body. Clinically important examples include: Circle of Willis (in the brain) Coronary: anterior interventricular artery and posterior interventricular artery of the heart; Scapular anastomosis (for the subclavian vessels)
In human anatomy, the left and right posterior communicating arteries are small [1]: 471 arteries at the base of the brain that form part of the circle of Willis. Anteriorly, it unites with the internal carotid artery (ICA) (prior to the terminal bifurcation of the ICA into the anterior cerebral artery and middle cerebral artery ); posteriorly ...
In case of narrowing of other arteries of the circle of Willis or the arteries supplying the circle, the anterior communicating artery can provide a way to supply blood to the opposite (affected) side of the circle. This can often preserve the cerebral blood supply well enough to avoid the symptoms of ischemia. [7]
The anterior and posterior circulations meet at the circle of Willis, pictured here, which rests at the top of the brainstem. Inferior view. The posterior cerebral circulation is the blood supply to the posterior portion of the brain, including the occipital lobes, cerebellum and brainstem. It is supplied by the following arteries:
Collateral circulation is the alternate circulation around a blocked artery or vein via another path, such as nearby minor vessels. [1] It may occur via preexisting vascular redundancy (analogous to engineered redundancy), as in the circle of Willis in the brain, or it may occur via new branches formed between adjacent blood vessels (neovascularization), as in the eye after a retinal embolism ...
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In circulatory anastomoses, many arteries naturally anastomose with each other; for example, the inferior epigastric artery and superior epigastric artery, or the anterior and/or posterior communicating arteries in the Circle of Willis in the brain. The circulatory anastomosis is further divided into arterial and venous anastomosis.