Hepatic portal system
From IKE
Contents |
Veins
Composition
The hepatic portal vein receives:
- Superior mesentaric
- Inferior mesentaric
- Splenic - drains areas supplied by the celiac trunk
- Gastric
Course
The inferior mesenteric vein usually joins the splenic vein behind the pancreas, but it may join the superior mesenteric vein instead.
The portal vein is formed by the union of the superior mesenteric and splenic veins, behind the neck of the pancreas. From here, it ascends posterior to the first part of the duodenum, into the free edge of the lesser omentum to reach the porta hepatis, where it divides into the right and left portal veins, destined to the right and left lobes of the liver. The right and left gastric veins often open directly into the portal vein, while the right portal vein receives the cystic vein and the left receives paraumbilical veins.
The ligamentum venosum and ligamentum teres are also connected to the left portal vein.
Portal systematic anastomosis
Main Sites
- In the wall of the lower esophagus, between tributaries of left gastric vein and the azygous system (to superior vena cava)
- in the wall of the anal canal, between tributaries of the superior rectal vein and the middle and inferior rectal veins (to inferior vena cava via the internal iliac vein)
- around the umbilicus, between paraumbilical veins (in the falciform ligament) and epigastric veins (to superior vena cava via the axillary vein and inferior vena cava via the femoral vein)
- retroperitoneal, between tributaries of colic, pancreatic and duodenal veins and tributaries of systemic veins (e.g., lumbar and posterior intercostal) that drain the surrounding fascia and connective tissues.
Clinical significance
In cases of portal hypertension, bloodflow through the liver is impeded due to conditions such as cirrhosis of the liver. The presence of anastomotic channels between veins of the portal system and veins of the systemic (caval) system, and the fact that they are valveless, allows the portal blood to by-pass the liver by entering the caval system, instead.
Objectives
- name the veins which form the portal vein, describe its course and state its function
- list the main sites of anastomosis between the portal and caval (systemic) venous systems and state their clinical significance
