portal venous system

the portal vein

Formed by the union of the splenic and superior mesenteric vv.

• The inferior mesenteric v. empties into the splenic v.

• Upon reaching the liver at the porta hepatis, the portal vein divides into left and right portal vv. which end in capillaries known as the venous sinusoids of the liver.

• The GI tract has its own venous drainage system that carries blood to the liver

caval (systemic) system

blood processed by the liver enters back into this system via the hepatic veins at the superior and posterior part of the liver, which lead into the IVC

• drains blood from the rest of the body (limbs, head, body wall, etc.) except for the foregut, midgut and hindgut

portal-caval anastomoses

Provide alternative pathways for blood from the portal system to return to the systemic venous system if the liver or portal vein are obstructed.

• Liver diseases such as hepatitis, cirrhosis or cancer may block normal blood flow resulting in portal hypertension.

• Veins of the portal system do not have valves, so the blood flow can be reversed.

locations of anastomoses

• Esophageal vv.

  • Along the distal portion of the esophagus.

• Rectal vv.

  • the superior rectal branch of inferior mesenteric with the middle rectal branch of the internal iliac v. and the inferior rectal branch of the internal pudendal v. 

• Paraumbilical vv.

  • In the region of the umbilicus

caput medusae

disease where umbilical veins that have become enlarged due to blockages in the liver where the blood is backing up into the caval system through anastamoses

• Portal hypertension caused by liver disease

• Anastamoses form between the caval and portal systems

• Previously closed fetal vessels (umbilical veins) can recanalize

review of veins of the abdomen

• Inferior vena cava is to right side of vertebral column.

  • Vessels from left side of abdomen must travel a greater distance or drain into left renal vein (left suprarenal, testicular).

• Major veins are named the same as the arteries: lumbar to body wall; renal, suprarenal, testicular/ovarian,  and inferior phrenic

• Veins from the GI tract do NOT return to the IVC

• Hepatic veins: drain the liver, both the blood from the hepatic artery and the portal vein.

• The renal veins lie ventral to the renal arteries.

• Inferior vena cava formed by the merging of the common iliac vv.