Table 2011 The Azygos System
The superior vena cava receives extensive drainage from the thoracic and abdominal walls by way of the azygos (AZ-ih-goss) system (fig. 20.35).
Drainage of the Abdominal Wall
A pair of ascending lumbar veins receive blood from the common iliac veins below and a series of short horizontal lumbar veins that drain the abdominal wall. The ascending lumbar veins anastomose with the inferior vena cava beside them and ascend through the diaphragm into the thoracic cavity.
Drainage of the Thorax
Right side. After penetrating the diaphragm, the right ascending lumbar vein becomes the azygos25 vein of the thorax. The azygos receives blood from the right posterior intercostal veins, which drain the chest muscles, and from the esophageal, mediastinal, pericardial, and right bronchial veins. It then empties into the superior vena cava at the level of vertebra T4.
Left side. The left ascending lumbar vein continues into the thorax as the hemiazygos26 vein. The hemiazygos drains the ninth through eleventh posterior intercostal veins and some esophageal and mediastinal veins on the left. At midthorax, it crosses over to the right side and empties into the azygos vein.
The accessory hemiazygos vein is a superior extension of the hemiazygos. It drains the fourth through eighth posterior intercostal veins and the left bronchial vein. It also crosses to the right side and empties into the azygos vein.
Figure 20.35 Veins of the Azygos System.
25unpaired; from a = without + zygo = union, mate 26hemi = half
Saladin: Anatomy & I 20. The Circulatory System: I Text I © The McGraw-Hill
Physiology: The Unity of Blood Vessels and Companies, 2003
Form and Function, Third Circulation Edition
Chapter 20 The Circulatory System: Blood Vessels and Circulation 787
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