Definition of Circle of Willis and Function

Circle of WillisCircle of Willis is a looped network (anastamosis) of arteries at the base of the brain.

Branches of the internal carotid arteries form the front of the circle and branches of the posterior cerebral arteries form the back of the circle, with smaller arteries, collectively called the communicating arteries, branching from them.

The circle of Willis is a unique vascular structure in the body that provides an extended safety net of redundancy for the brain’s blood supply; the closest analogous configuration is that of the coronary arteries which supply the heart.

Even if damage occurs to one or two of the circle of Willis’s anastomosed arteries, blood flow to the brain continues

The base of the skull protects this arterial network. The circle of Willis, because of its complexity, varies anatomically among individuals and is a common site for congenital vascular anomalies (malformations of the blood vessels).

For further discussion of cardiovascular structure and function, please see the overview section “The Cardiovascular System.”


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