الفهرس 
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Abstract
The portal system includes all the veins that collect blood from the abdominal part of the alimentary tract, spleen, pancreas and gall bladder the portal vein collects blood from the splanchnic area and transports blood to the liver. The arteries supplying this blood are the non hepatic branches of the celiac axis and the superior and inferior mesentric arteries (Leon—Schiff, 1982). The portal vein is formed by the union of superior mesentric vein and splenic vein just posterior to the head of pancreas at about the level of the second lumbar vertebra, it extends slightly to the right of mid line for a distance of 5.5-8 cms to the porta hepatis. The portal vein has segmental intrahepatic distribution. The superior mesentric vein is formed by tributaries from the small intestine, colon and head of pancreas. The splenic veins are 5-15 channels orginate at the splenic hilum and the veins near the tail of pancreas unite with the short gastric veins to form the main splenic vein this proceeds in transverse direction in the body and head of pancreas lying below and in front of the artery, it receives numerous tributaries from the head of pancreas and the left gastro-epipolic vein, enters it near the spleen. The inferior mesentric vein bringing blood from the left part of the colon and rectum usually enters its medial third. Occasionally it enters the junction of superior mesentric and splenic veins. The portal venous blood passes through one capillary system, in the splanchnic viscera and
leads to another capillary system, the hepatic sinusoids portal veinous blood differs from other most venous blood in being under slightly high pressure, in being less depleted in oxygen because of the relatively high blood flow through the splanchnic area and in containing many nutrients and bacterial waste products from the digestive tube that are enroute to liver (1-lollinshead, 1974).
The tributaries of the portal vein are
1 ) Splenic vein.
2 ) Left gastric vein.
3 ) Right gastric vein.
4 ) Superior nesentric vein.
5 ) Para-umblical veins.
6 ) Cystic veins drain the gall bladder.
The normal fasting hepatic blood flow approximates 1.500 ml./minute, the high pressure hepatic arterial and low pressure portal venous stream unite at the level of hepatic sinusoids. The best estimates aavilable indicate that about two thirds of hepatic blood flow and about + of total oxygen consumption is supplied by the portal vein while the hepatic artery contributes to the remainder (Schent et al., 1962).