Expansion
Upper oesophagus drains systemically; the lower third drains to the left gastric vein and the portal system
Expansion
- Upper third - inferior thyroid veins, to the systemic circulation
- Middle third - azygos and hemiazygos veins, to the systemic circulation
- Lower third - oesophageal branches of the left gastric vein, to the portal circulation
The submucosal plexus of the lower oesophagus is therefore a watershed between two venous systems. When portal pressure rises in cirrhosis, blood is forced retrogradely up this plexus into the azygos system, distending thin-walled submucosal veins into varices.
The same principle produces the other portosystemic anastomoses: the periumbilical veins (caput medusae) and the superior versus middle and inferior rectal veins.