47. Circle of Willis
he Circle of Willis is a ring of arteries at the base of the brain that connects the internal carotid arteries and the vertebrobasilar system, ensuring continuous blood flow to the brain. It acts as a "fail-safe" system, allowing blood to be rerouted to bypass blockages in one of the major arteries supplying the brain. This collateral circulation reduces the risk of ischemic events, such as stroke. Anterior Circulation: Internal carotid arteries, anterior cerebral arteries, and the anterior communicating artery. Posterior Circulation: Vertebral arteries, basilar artery, posterior cerebral arteries, and the posterior communicating arteries.