The brain vascular network. Left: the network of brain vasculature (public domain image) . Middle: vascular organization of the cerebral cortex . Arterioles (pink) penetrate the brain cortex and branch out into dense capillary beds that feed an active region of the brain (highlighted in red). Venules (dark red) take away the blood from the brain capillary beds. The image by by  is licensed under CC BY 3.0. Right: capillaries. A capillary bed consists of a small network of capillaries. The brain capillaries are fed with oxygen and nutrients by the blood flow from the general blood circulation through the arteries and arterioles. Waste products are carried away from the brain capillaries by blood flow back into the heart through the venules and veins.