What does this brief paragraph mean with regards to collateral circulation in systemic venous system?

This is to do with the links between the portal and systemic circulations, which are normally small. However, if the portal vein is obstructed, as in cirrhosis of the liver, the blood from the intestines must find another way back to the heart. It goes back to the vessels which open up around the umbilicus, and drains into the inferior epigastric veins and thence to the IVC. Other potential collateral circulations also open up, notably around the oesophagus. This one is fragile and frequently bleeds spectacularly, but the others, including the lumbar vein linkages, are of lesser significance.