Usually in the the vascular system both artery and vein go together .It is an irony in pulmonary circualtion these two never go together .Another paradox is that pulmonary artery carries the most deoxygenated blood and pulmonary vien carries the purest form of blood in the entrie body , probably God has kept them widely seperated as communication between them seriously affect the physiology.
Dr.S.Venkatesan MD 