# Collateralization --- **Collateralization** or **collateral circulation** is a redundancy in a [[circulatory system]] that allows fluids to have alternate routes to certain tissues. This happens naturally in some areas (such as the [[cerebral circulation|circle of Willis]] in the brain), but can also be triggered to form in the case of a slow forming occlusion, such as with [[atherosclerosis]]. It is a compensatory mechanism, not to be confused with [[coronary artery disease#Remodeling|negative remodeling]] of the coronary arteries, which is maladaptive, and causes the arterioles to shrink. In the [[brain]] the Circle of Willis's main job is to be a collateral vessel, allowing blood to flow to all areas of the brain, allowing it to bypass if there is an occlusion that would cause an [[ischemic stroke]]. ___