The hepatic portal vein is characterized by the basic absence of venous valves and capillaries at both ends of the system. 1. Basically no venous valves: the main function of venous valves is to control the flow of blood in a certain direction, and the absence of venous valves allows the blood to flow in the direction of high pressure. This is a characteristic of the hepatic portal vein. 2. Both ends of the system are capillaries: one side of the anal vein enters the liver, the other side is formed by the confluence of the superior mesenteric vein and the splenic vein. It mainly collects blood from the capillaries of the stomach, intestines, pancreas and spleen, so both ends of the portal vein are capillaries. When the portal vein is hypertensive or the patient has cirrhosis, the increased pressure makes the blood flow backward, causing the opening of collateral circulation, which easily leads to abnormal symptoms such as esophageal and gastric fundus varices. It is recommended that patients with portal vein anomalies should seek medical attention in a timely manner.