Notes for this section are being prepared.

Blood vessels of the lungs

The lungs are connected to the heart by blood vessels that carry blood in opposite directions:

The pulmonary artery carries blood from the heart to the lungs. It arrives at the lungs.
The pulmonary vein carries blood from the lungs back to the heart. It leaves the lungs.

When identifying these vessels in a diagram, follow the direction of blood flow in relation to the lungs. A vessel carrying blood towards the lungs is the pulmonary artery; one carrying blood away from the lungs towards the heart is the pulmonary vein.

Blood vessels of the kidney

Blood reaches the kidney through one main vessel and leaves through another. These vessels are named according to the direction in which they carry blood:

The renal artery carries blood to the kidney from the arterial system.
The renal vein carries blood away from the kidney to the venous system.

In a diagram or image, locate the vessels connected to the kidney. The vessel entering from the arterial system is the renal artery; the vessel leaving to join the venous system is the renal vein. If arrows show blood flow, use their direction to distinguish the blood input from the blood output.

Blood vessels of the liver

Three main blood vessels connect the liver to the circulation. Two carry blood into the liver, while one carries blood away from it.

The hepatic artery carries blood to the liver from the arterial circulation.
The hepatic portal vein carries blood to the liver from the digestive organs.
The hepatic vein carries blood away from the liver.

In a diagram, identify each vessel by the direction in which it carries blood relative to the liver. The hepatic artery and hepatic portal vein enter the liver; the hepatic vein leaves it. Despite its name, the hepatic portal vein carries blood towards the liver, not away from it.