The anterior communicating artery is found on the underside of the human brain. Situated just in front of the spinal cord, this blood vessel links the left and right anterior cerebral arteries, which deliver oxygenated blood to the medial or inner aspects of the frontal lobe and upper parietal lobes. Together, the anterior communicating artery and cerebral arteries form the anterior curve of the Circle of Willis, also known as the cerebral arterial circle, in the cerebrum.
As the blood vessels of the brain are symmetrical — each side is a mirror image of the other, were the brain folded in half lengthwise — most arteries are paired. The anterior communicating artery, however, is a singular vessel. It laterally cuts across the space known as the longitudinal fissure, the split down the midline of the anterior cerebrum that divides the brain into right and left halves. Found where the longitudinal fissure begins, roughly one-third of the way back from the front end of the brain, the anterior communicating artery runs between the paired anterior cerebral arteries.
Only a few centimeters in length, this vessel closes the gap between the anterior cerebral arteries, creating a loop known as the Circle of Willis that distributes oxygenated blood throughout the brain. Arteries are distinguished from veins in that they carry blood rich with oxygen and nutrients away from the heart, while veins return to the heart blood that has been drained of its oxygen and nutrients. As such, the blood tends to flow linearly and in one direction. The Circle of Willis is a redundant blood-distribution system, meaning that if anything happens to cause a blockage in or reduce blood flow to one or more arteries in the circle, the other vessels can step in to deliver blood wherever it is needed so that the brain is not deprived of oxygen.
Arising from the anterior cerebral arteries on either end, the anterior communicating artery gets its blood flow from these vessels, which in turn receive blood from a major vessel known as the internal carotid artery. Blood flows into the Circle of Willis from the internal carotid on either side of the brain. Once in the loop, however, this blood flow is not unidirectional. Rather, the blood fills these vessels, perfusing the tissues of the brain in all directions via a network of tiny arterioles and even smaller capillaries distributed throughout.