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Azygos venous system

The azygos system of veins (azgyos venous system) consists of several longitudinal vessels on both sides of the spine that collect venous blood from the viscera of the mediastinum, and from structures of the back, as well as the thoracic and abdominal walls. The veins forming the azygous venous system ascend and empty into the superior vena cava. This venous system serves as an important anastomotic pathway that can return deoxygenated blood to the heart from the lower part of the body if the inferior vena cava is blocked.

The major veins of the azygos venous system include: on the left - the azygos vein, and on the right, its two tributaries - the hemiazygos vein and the accessory hemiazygos vein. The origin, course, tributaries, anastomoses, and termination of these vessels are quite variable.

Some veins from the thoracic viscera (internal organs of the thorax) may also drain into the azygos venous system. The veins of the azygos system also form anastomoses with abdominal veins. The longitudinal vessels of this venous system are interconnected through anastomoses from side to side at various points throughout their course.