20th February 2024

Thoracic, abdominal and pelvic cavity

Within the thoracic cavity, the main veins that pass through are the inferior vena cava and the azygos venous system. The azygous venous system consists of the azygous vein, hemiazygos vein and accessory hemiazygos vein. The azygos vein can arise from the lumbar azygos vein or directly from the inferior vena cava at the renal vein level. It courses within the posterior mediastinum and arches over the right pulmonary hilum before draining into the SVC. Its major tributaries are the hemiazygos and accessory hemiazygos vein. The hemiazygos vein drains from the lumbar ascending and subcostal veins from the 9-11 ribs. This will drain back to the azygos vein at the level of T8. The accessory hemiazygos vein will drain blood from the 5th-8th ribs and the left bronchial vein. It empties into the azygos vein at T7.

The pelvic venous drainage occurs through the internal iliac vein. It receives the venous return from the majority of the pelvic organs. It will merge with the external iliac vein at the level of the pubic symphysis to form the common iliac vein.

The systemic venous drainage from the abdomen occurs through the IVC. The IVC is formed from the union of the common iliac veins at the level of L5. This travels superiorly and will drain into the right atrium. It receives blood from the common iliac, lumbar, renal, right gonadal, right suprarenal, and hepatic veins.

Image Source: Wikimedia Commons (2013). 2132 Thoracic Abdominal Veins, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/2/28/2132_Thoracic_Abdominal_Veins.jpg (Accessed: 9 January 2024).

Venous drainage of the GI tract, spleen, pancreas and gallbladder is carried out via the portal venous system. The union of the splenic vein and superior mesenteric vein forms the portal vein. The portal vein divides into the right and left portal vein as it enters the liver, delivering nutrient-rich venous blood into the liver.

Image Source: Wikimedia Commons (2013). 2138 Hepatic Portal Vein System, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/c/cf/2138_Hepatic_Portal_Vein_System.jpg (Accessed: 9 January 2024).