Blood supply of the brain
The human brain has the highest demand for oxygen of any tissue in the human body. About fifteen to twenty percent (15-20%) of the daily cardiac output is utilized by the brain. Owing to the high oxygen and nutrient demand of the organ, it is supplied by two arterial systems: the internal carotid system anteriorly, and the vertebrobasilar system posteriorly.
The venous drainage of the brain does not follow the arteries of the brain. Instead, venous blood of the brain drains into the dural sinuses, which subsequently drain to the internal jugular vein. The veins of the brain are divided into superficial cerebral veins and internal cerebral veins, depending on whether they drain the superficial structures of the brain or the deep structures.
Arteries of the brain
The arterial supply of the brain is derived from two primary sources: the internal carotid and vertebral arteries. The internal carotid arteries and their branches supply blood to the majority of the forebrain giving them the classification of the anterior cerebral circulation or the internal carotid system.
The vertebral arteries and their major branches supply blood to the spinal cord, brainstem and cerebellum, and a significant part of the posterior cerebral hemispheres (usually the occipital and inferior temporal lobes). The vertebral arteries and their branches are commonly referred to as the vertebrobasilar system or the posterior cerebral circulation.
The cerebral arterial circle (of Willis) is an anatomical structure that provides an anastomotic connection between the anterior and posterior circulations, providing collateral flow to affected brain regions in the event of arterial incompetency.
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Veins of the brain
The brain is an especially well-vascularized organ, receiving approximately twenty percent of cardiac output. The veins of the brain drain the blood from the entire brain as well as the surrounding structures (meninges, eyeballs etc). The drained blood is then first returned to the dural venous sinuses and then the internal jugular vein. Structurally, the veins of the brain lack a muscular layer (tunica media), which allows them to expand and collapse substantially. There are two types of venous systems that drain the blood from the brain. These are the superficial (external) venous system and the deep (internal) venous system.
Venous drainage of the cerebellum is achieved by the superior and inferior cerebellar veins which drain into the great cerebral vein (of Galen), the straight sinus, the superior petrosal sinus, or the sigmoid sinus.
Veins of the brainstem form an intricate plexus deep to the arteries of the brainstem and drain to the veins of the spinal cord, basal vein, great cerebral vein (of Galen), cerebellar veins and/or the dural venous sinuses.
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Dural venous sinuses
The dural venous sinuses are major vascular channels contained between the meningeal and periosteal layers of the dura mater. Most of the major dural venous sinuses are found adjacent to the falx cerebri and tentorium cerebelli. Major dural venous sinuses include the superior sagittal sinus, inferior sagittal sinus, straight sinus, transverse sinus, sigmoid sinus and superior petrosal sinus.
The main function of the dural venous sinuses is to drain all venous blood within the cranial cavity with the ultimate point of drainage being the internal jugular vein. In addition, the dural sinuses also drain cerebrospinal fluid (CSF) via arachnoid granulations.
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