Question

Why does the pulmonary vein not have valves?

All other veins have valves to prevent backflow so why does pulmonary vein not have a valve?

Answer 1

The pulmonary veins do not have valves because the pressure exerted by the heart is strong enough to keep the blood flowing in one direction.

Explanation:

There are four pulmonary veins, two from each lung.

The left and right superior and inferior pulmonary veins carry oxygenated blood from the lungs back to the left atrium of the heart.

They differ from other veins in that they do not have valves.

The distance from the heart to the lungs and back again is so short compared to the systemic circulation that the heart contraction is enough to keep the blood flowing in one direction.

Thus, the pulmonary veins do not need valves.