A number of connections occur between the portal and systemic circulations. When the direct pathway through the liver becomes congested (such as in cirrhosis) the pressure within the portal vein rises and under these circumstances the porto-systemic anastomoses form an alternative route for the blood to take. The sites of porto-systemic anastomosis include:
• The lower oesophagus (p. 11): formed by tributaries of the left gastric (portal) and oesophageal veins (systemic via the azygos and hemi-azygos veins).
• The anal canal: formed by the superior rectal (portal) and middle and inferior rectal veins (systemic).
• The bare area of the liver: formed by the small veins of the portal system and the phrenic veins (systemic).
• The periumbilical region: formed by small paraumbilical veins which drain into the left portal vein and the superficial veins of the anterior abdominal wall (systemic).
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