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Anatomy · Heart & blood vessels

Pulmonary vein

Carries oxygenated blood from the lungs

Thorax · pulmonary circulation

There are normally four pulmonary veins, two from each lung, and they carry freshly oxygenated blood back to the left atrium. Together with the umbilical vein in the foetus they are the classic exceptions to the rule that veins carry deoxygenated blood. They enter the back of the left atrium and have no valves.

How to spot them

  • ▸Two on each side, right superior and inferior and left superior and inferior, entering the posterior wall of the left atrium
  • ▸Short trunks, only 1–2 cm long, running from the hilum of each lung
  • ▸The right pair passes behind the right atrium and the superior vena cava
  • ▸The atrial muscle extends a short way into the walls of the veins, which matters in atrial fibrillation

What to know

Veins that carry oxygen-rich blood, entering the back of the left atrium

Pulmonary veins.

Normally four in number, two from each lung

Pulmonary veins — right superior and inferior, left superior and inferior.

Along with the umbilical vein, these are the only veins in the body carrying oxygenated blood

Pulmonary veins.

Sleeves of atrial muscle extend along their walls, and ectopic beats arising there commonly trigger atrial fibrillation

Pulmonary veins — targeted in catheter ablation (pulmonary vein isolation).

Lacking valves, they open into the left atrium in the smooth-walled posterior part of its wall

Pulmonary veins — the smooth part of the left atrium.

The right pair passes behind the right atrium and the superior vena cava to reach the left atrium

Pulmonary veins.

They lie below and in front of the corresponding pulmonary arteries in the lung hilum

Pulmonary veins — vein lowest at the hilum.

Key ideas

  • Naming by function, not oxygen content: arteries lead away from the heart, veins lead toward it. The pulmonary circuit is where the usual colour code reverses.
  • Backward pressure from a failing left heart is transmitted into these veins and raises pulmonary capillary pressure, causing pulmonary oedema.

Quick-fire facts

  • •Most people have four pulmonary veins (right superior, right inferior, left superior, left inferior); variation is common, e.g. a third right vein.
  • •They open into the smooth posterior wall of the left atrium and have no valves.
  • •In the hilum of the lung, the pulmonary veins lie lowest and in front of the bronchus; the artery lies above the bronchus on the left.
  • •Blood in them is around 98–100% saturated with oxygen.
  • •Pulmonary vein isolation by catheter ablation is a standard treatment for paroxysmal atrial fibrillation.
  • •The oxygen-rich blood is carried on to the left ventricle via the mitral valve.
  • •In the foetus, oxygenated blood from the placenta travels in the umbilical vein instead.
  • •Total anomalous pulmonary venous connection is a congenital defect in which they drain to the right side of the heart.

Drill it — 7 cards

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Sources