L03 - Stomach
3. Differentiate between portal venous & hepatic arterial circulation to and from the liver.
Portal systems are vessels that link sets of capillary beds. The hepatic portal system is a venous portal system consisting of all veins that drain the gastrointestinal tract (GIT) from the abdominal esophagus to the superior rectum. These veins coalesce into the hepatic portal v. which delivers blood from the capillary beds of the GIT to capillary beds of the hepatic sinusoidal cells. As the hepatic portal system connects capillary beds, it is a separate system from the caval system (those veins which drain into the vena cavae). Blood from the hepatic sinusoidal cells is delivered back into the caval system via hepatic vv. draining into the inferior vena cava.
The hepatic portal v. typically originates as a union of the superior mesenteric v. with the splenic v. in the transpyloric plane (approximately at L1), posterior to the neck of the pancreas. The hepatic portal v. ascends to the liver within the hepatoduodenal ligament with the (common) bile duct and the hepatic a. proper. These three elements are often referred to as the portal triad.
Typically, three (left, middle, & right) hepatic vv. drain blood of the liver to the inferior vena cava. These may be found draining into the portion of the inferior vena cava that passes through the fissure of inferior vena cava of the liver.