The lymphatic system is like a city's network of canals, through which water slowly moves, carrying away waste from tissues. But it has no single pump-heart. Instead, along the vessels are placed small station-locks — lymphangions. Each such lock squeezes itself like a fist and pushes fluid onward. How they coordinate their work has long remained a mystery.
A new mathematical model for the first time combined the physics of fluid flow and the chemistry inside the cells of the lock. The equations showed: the key to the rhythm is two substances, calcium and nitric oxide. Calcium makes the lock's muscles contract, while nitric oxide makes them relax. Their opposition is like a seesaw: first one outweighs, then the other, and so on without stopping.
The authors found conditions under which a stable oscillation — that very rhythmic "pulse" of the lymphatic vessel — is guaranteed to arise in the system. This matches what is observed in experiments: lymphatic vessels contract at a frequency of about 10–20 times per minute, even if they are isolated. The model allows predicting how disruptions in calcium or nitric oxide chemistry can lead to lymph stasis and edema. And thus, a target for future drugs emerges.
The lymphatic system pumps about 3 liters of fluid per day — more than half the volume of blood in the human body.