Thoracic Veins
Blood from the systemic circulation of the body is returned to the right atrium of the heart by the large veins called the superior and inferior vena cava. Deoxygenated blood used by heart tissue itself is returned to the right atrium by a coronary vein termed the coronary sulcus, and a number of smaller coronary veins that also return blood directly to the right atrium.
The inferior vena cava, which runs through the thorax, returns blood from the abdomen, legs, and hepatic circulation (the hepatic portal system of the liver) runs along the frontal (anterior) side of the spine and lies next to the abdominal aorta (a continuation of the thoracic aorta). After passing through the diaphragm that separates the thoracic from the abdominal cavity, the inferior vena cava continues onward to the heart for approximately 1 in. (2.5 cm) before it fuses with, and empties its contents into, the right atrium of the heart along with the superior vena cava.
The superior vena cava returns blood from the upper half of the body, including the head, neck, upper limbs, and the thoracic region itself. The superior vena cava is a large diameter vein that is almost 3 in. (approximately 7 mm) long running from about the level of the first rib to the right atrium of the heart. Within the right atrium of the heart, blood from the superior vena cava mixes with blood from the inferior vena cava and blood returned from the coronary circulation.
The superior vena cava is formed from the fusion of the brachiocephalic veins--also termed the innominate veins--are two large veins that run on each side of the neck. The left brachiocephalic vein is formed by the fusion of the left subclavian and left jugular vein. Correspondingly, the right brachiocephalic vein is formed by the fusion of the right subclavian and right jugular veins. The left and right subclavian veins return blood from the corresponding left or right arm and shoulder region (upper limb) and the jugular veins return blood from the head and neck regions. The brachiocephalic veins, also return blood from the thyroid and thorax proper (e.g., rib or intercostals veins).
Other major thoracic veins include the internal thoracic veins (also termed the mammary veins), the inferior thyroid veins, bronchial veins, vertebral veins, and intercostal veins.
The azygous vein runs down the right side of the vertebral column. Although the azygous vein actually begins in the lumbar region near the renal veins, it travels upward to pass through the diagram and eventually fuse with the superior vena cava. Running through the posterior mediastinum, the azygos vein receives venous contributions from a number of smaller posterior intercostals veins. A hemizygous vein runs alongside the left side of the vertebral column to terminate in a superior intercostal vein. Connections between the azygos and hemiazygos veins are not uncommon, and they occur at variable levels.
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