The brain is supplied with blood by the vertebral a. (which branches into the Anterior spinal a., Posterior spinal a., and Posterior inferior cerebellar a.), the basilar a. (which branches into the Anterior inferior cerebellar a., Superior cerebellar a. Posterior cerebral a., and Posterior communicating a.), and the internal carotid a. (which branches into the Ophthalmic a., Middle cerebral a., Anterior cerebral a., and Anterior communicating a.). This collection of arteries is called the cerebral arterial circle (circle of Willis) and is designed to optimize circulation to the brain and maintain full function even if one or two arteries were damaged. The internal cartoid a. and basilar a. branch from the right common cartoid a., and the vertebral a. originates at the right subclavian a. Both of these came from the brachicephalic a., the first artery on the aortic arch which comes from the left ventricle of the heart. The arteries in the brain as a collective form what is commonly referred to as the Circle of Willis or arterial circle. The Circle of Willis is designed to circulate enough blood through the brain even if one or even two arteries were to stop functioning.
Most blood draining from the head and neck enters three pairs of veins: internal jugular veins, external jugular veins, and vertebral veins. Although several of these veins share the same name as particular arteries their paths differ greatly. Most veins from the brain drain into the dural sinuses. The superior and inferior sagittal sinuses lie between the two hemispheres and drain posteriorly into the transverse sinuses, which in turn drain into the sigmoid sinus and into the internal jugular veins it leaves the skull through the jugular foramen. The internal jugular vein then enters the left brachiocephalic vein and then into the superior vena cava which leads into the right atrium.
The stomach is supplied blood by the left gastric artery, a branch of the coeliac a. This artery supplies the lower third of the esophagus and the upper right portion of the stomach. The right gastric artery, a branch of the hepatic a., which supplies the lower right portion of the stomach. The short gastric a., branches of the splenic a. at the hilus of the spleen. These arteries supply the fundus of the stomach. The left gastroepiploic a., a branch of the splenic a. supplies the superior part of the greater curvature of the stomach. The right gastroepiploic a., a branch of the gastroduodenal branch of the hepatic artery supplies the inferior part of the lesser curvature of the stomach. These arteries come from the thoratic aorta, which originates in the left ventricle, ascends, and curves inferiorly.
The stomach drains its blood into the left and right gastric v., which drains into the portal vein. The short gastric veins and left gastroepiploic v. drain into the splenic v., which drains into the portal vein. The right gastroepiploic v. drains into the superior mesenteric vein. The final vessel before reaching the right atrium is the inferior vena cava. Veins usually carry blood straight to the atria of the heart, but those of the abdominal tissues are exceptions. These come from networks in the stomach, intestines, pancreas, and spleen, and carry blood from these organs through a portal vein to the liver. There, the blood enters capillary-like hepatic sinusoids. This is called the hepatic portal system.
There are several differences between the blood circulation of the brain and the stomach and spleen. The differences relating to arteries is that the brain requires the arteries to pump the blood against gravity, so the source for itís arteries is very close to the heart, while the stomach and spleen require less effort to circulate blood from the heart. There are also more blood vessels around the brain than the stomach. The circle of Willis is a protective precaution, which enables the brain to function properly even with one or two damaged arteries, and the stomach has no such defense. There were also a lot of differences in the veins of the brain and the veins of the stomach and spleen. The main difference was that the blood from the brain drained into sinuses was led into the internal jugular vein which was directed into the subclavian vein, into the superior vena cava, and into the right atrium, while the stomach and spleen have the hepatic portal system, which takes the blood into the liver twice for filtration before returning into the inferior vena cava, and then to the right atrium. Also the veins in the stomach and spleen have to travel upwards to reach the heart and the veins from the brain just have to drain into it, which means that there are probably more valves in the veins of the stomach and spleen than in the veins of the brain.