The function of venous valves is to promote venous reflux from gravity, so there are more valves in the extremities, which are most affected by gravity, and more in the lower extremities than in the upper extremities, while other parts can complete reflux smoothly due to gravity itself, which generally does not have valves. Veins that do not have valves such as intracranial veins, jugular veins, superior vena cava, inferior vena cava, and veins in the viscera do not have valves, and veins that do not have valves generally do not have varicosities due to gravity, but they do not have valves, which can cause infection to enter the inferior veins more easily.