SN1 SHORT NOTE 5M ★ High-yield

Describe the formation and tributaries of the portal vein. Add a note on portal hypertension and portosystemic anastomoses.

Anatomy · 1st Professional — Pre-Clinical

The portal vein carries venous blood from the abdominal part of the alimentary canal, the spleen, pancreas and gall bladder to the liver.

The inferior mesenteric vein usually joins the splenic vein
Tributaries — left and right gastric, cystic, para-umbilical and superior pancreaticoduodenal veins
It has NO valves — which is why raised pressure is transmitted freely backward into its tributaries
It begins and ends in capillaries — a portal system by definition

Site	Portal tributary	Systemic tributary	Clinical result
Lower oesophagus	Left gastric vein	Oesophageal veins into the azygos	Oesophageal varices — the most dangerous
Anal canal	Superior rectal vein	Middle and inferior rectal veins	Haemorrhoids
Umbilicus	Para-umbilical veins	Superficial epigastric veins	Caput medusae
Retroperitoneal (of Retzius)	Colic veins	Retroperitoneal and renal veins	Retroperitoneal varices
Bare area of the liver	Portal branches	Phrenic veins	—
Patent ductus venosus	Left portal branch	Inferior vena cava	Rare

Site of obstruction	Causes
Pre-hepatic	Portal vein thrombosis, congenital atresia, extrinsic compression
Hepatic	Cirrhosis (the commonest), schistosomiasis, congenital hepatic fibrosis
Post-hepatic	Budd–Chiari syndrome, constrictive pericarditis, right heart failure

Splenomegaly and hypersplenism
Ascites — from raised portal pressure and hypoalbuminaemia
Haematemesis and melaena from ruptured varices
Caput medusae — dilated veins radiating from the umbilicus, with flow away from the umbilicus, distinguishing it from inferior vena caval obstruction where flow is upward
Hepatic encephalopathy — portal blood bypasses the liver, so ammonia and other toxins reach the brain

Endoscopic band ligation or sclerotherapy is the first-line treatment of bleeding varices; beta blockers reduce portal pressure for prevention
Tips (transjugular intrahepatic portosystemic shunt) creates a channel between a hepatic vein and a portal branch, decompressing the system — but precipitates encephalopathy by diverting blood past the liver
The portal vein carries no oxygenated blood but 70% of hepatic flow, which is why portal vein thrombosis is better tolerated than hepatic artery thrombosis after transplantation
Liver metastases from gastrointestinal cancers arrive by the portal vein — the anatomical reason the liver is the commonest site

All questions in Abdomen