Portal hypertension means increased blood pressure in the hepatic portal system - or portal venous system.
Most commonly, this happens because of hepatic cirrhosis, which is when the liver tissue is replaced by fibrotic, functionless tissue.
Now, the portal venous system comprises the portal vein and its tributaries - namely, the splenic, and mesenteric veins.
This blood contains all the nutrients absorbed in the GI tract, but it also carries toxins that the liver metabolizes so that they can be safely excreted by the kidneys.
Once the liver processes all these substances, it sends the blood to the heart, through the inferior vena cava, to enter the systemic venous system.
Now, there’s a few points in the boundaries of the hepatic portal system, where it could be connected with the systemic venous system that collects blood from the rest of the body: the inferior portion of the esophagus, the superior portion of the anal canal, and the round ligament of the liver - which used to be the umbilical vein during fetal life.
At birth, the umbilical cord is cut, and the umbilical vein collapses to form the round ligament.
Normally, the round ligament stays shut because pressures in the portal venous system and the systemic venous system are the same, between 5 and 10 Millimeters of Mercury
But in some situations, an obstruction may prevent blood flow from the portal vein towards the inferior vena cava.