Unlike the cardiovascular system, the lymphatic system lacks a central pump and relies on passive movement.

“Here's a critical feature of the lymphatic system that is different from the cardiovascular system, which is, there's no pump. In the cardiovascular system, you have a pump. You have a heart that can generate a lot of force to move that liquid out through the arteries and back through the veins, and you've got a lot of mechanical force coming from that heart. The lymphatic system doesn't have that at all. On its own, it's a passive system, no pump, and it's fighting gravity all the time.”