Formation of the trunk and main roots
The portal vein (V. portae hepatis) is formed posterior to the head of the pancreas (Pancreas). Its trunk is formed by the union of large vessels, each draining a specific region of the abdominal cavity:
- Superior mesenteric vein (V. mesenterica superior). Drains blood from the small intestine and the right half of the large intestine. Its basin includes the jejunal and ileal veins (Vv. jejunales et ileales), as well as colic vessels: the ileocolic vein (V. ileocolica) with the appendicular vein (V. appendicularis), and the right and middle colic veins (V. colica dextra and V. colica media). Additionally, it receives the pancreaticoduodenal vein (V. pancreaticoduodenalis) and the right gastro-omental vein (V. gastroomentalis dextra).
- Splenic vein (V. splenica). Drains the spleen (Splen), part of the pancreas via pancreatic veins (Vv. pancreaticae), and the fundus of the stomach via short gastric veins (Vv. gastricae breves). It also receives the left gastro-omental vein (V. gastroomentalis sinistra).
- Inferior mesenteric vein (V. mesenterica inferior). Collects venous blood from the left half of the large intestine via the left colic (V. colica sinistra), sigmoid (Vv. sigmoideae), and superior rectal (V. rectalis superior) veins. As an anatomical variant, it frequently drains into the splenic vein.
Direct tributaries from the stomach
Certain vessels do not belong to the basins of the three main roots, but drain directly into the trunk of the portal vein or its main branches. These include the gastric veins:
- Left gastric vein (V. gastrica sinistra). Runs along the lesser curvature of the stomach and is of critical importance as it forms anastomoses with the esophageal veins (Oesophagus).
- Right gastric vein (V. gastrica dextra). Connects (anastomoses) with the left gastric vein.
- Prepyloric vein (V. prepylorica).
Intrahepatic circulation
Upon reaching the porta hepatis (Hepar), the main vascular trunk divides into two large branches: the right (R. dexter v. portae hepatis) and the left (R. sinister v. portae hepatis). In this same region, the cystic vein (V. cystica), draining the gallbladder, and the paraumbilical veins (Vv. paraumbilicales), running within the round ligament of the liver, join the portal system.
Inside the hepatic tissue, venous blood flows through a specialized network of venous capillaries (sinusoids). After completing all clearance and metabolic processes, the blood collects into the hepatic veins (Vv. hepaticae). They direct the blood flow into the inferior vena cava system (V. cava inferior), returning it to the heart.
Clinically Important Anastomoses
Of particular practical significance are the regions where the branches of the portal system connect with the vessels of the systemic circulation — the so-called portosystemic anastomoses.
A striking example is the rectal venous plexus (Plexus venosus rectalis). Here, blood from the upper parts of the rectum drains into the portal system via the superior rectal vein (V. rectalis superior). At the same time, the middle and inferior rectal veins (Vv. rectales mediae et inferiores) empty into the caval system. Through them, the outflow goes into the internal iliac vein (V. iliaca interna), then into the common iliac vein (V. iliaca communis), and ultimately into the inferior vena cava.
Briefly: answers to topical questions
What are the portosystemic anastomoses?
The body contains the following portosystemic anastomoses, providing a connection between the portal vein system and the venae cavae:
- Rectal venous plexus (plexus venosus rectalis) — connects the superior rectal vein with the basin of the internal iliac vein (middle and inferior rectal veins).
- Umbilical portosystemic anastomosis — connects the paraumbilical veins (vv. paraumbilicales) with the veins of the anterior abdominal wall.
- Esophageal anastomosis — the left gastric vein (v. gastrica sinistra) anastomoses with the esophageal veins.
Which veins of the superior vena cava system do the esophageal veins anastomose with?
The esophageal veins (vv. oesophageales) drain blood into the azygos vein (v. azygos), which acts as a direct tributary of the superior vena cava. In the region of the abdominal part of the esophagus, these vessels form an important portosystemic anastomosis. They connect directly with the left gastric vein (v. gastrica sinistra), which runs along the lesser curvature of the stomach and empties directly into the trunk of the portal vein.
Which veins form the portosystemic anastomosis on the anterior abdominal wall?
The umbilical portosystemic anastomosis on the anterior abdominal wall is formed by the connection of paraumbilical veins with subcutaneous veins. It involves:
- Paraumbilical veins (vv. paraumbilicales) — carry blood from the portal vein system.
- Superior epigastric vein (v. epigastrica superior) and thoracoepigastric vein (v. thoracoepigastrica) — drain blood into the superior vena cava system.
- Inferior epigastric vein (v. epigastrica inferior) and superficial epigastric vein (v. epigastrica superficialis) — drain blood into the inferior vena cava system.
What anatomical structures form the portal triad at the porta hepatis?
In the porta hepatis (porta hepatis), the following main anatomical structures are located, forming the neurovascular bundle:
- Proper hepatic artery (a. hepatica propria).
- Portal vein (v. portae).
- Common hepatic duct (ductus hepaticus communis).
In addition to these elements, nerves and lymphatic vessels also pass through the porta hepatis region.
Class and exam questions
Where and how does the portal vein trunk begin?
The trunk of the portal vein is formed posterior to the head of the pancreas by the confluence of the superior mesenteric and splenic veins (the latter frequently receives the inferior mesenteric vein).
Which organs are drained by the portal vein system?
This system collects venous blood from the unpaired abdominal organs: the entire intestine (except the lower part of the rectum), stomach, pancreas, spleen, and gallbladder.
How does blood from the portal vein return to the systemic circulation?
After passing through the hepatic sinusoids (capillaries, purified blood enters the hepatic veins, which empty into the inferior vena cava, carrying blood directly to the right atrium.
What else to study on this topic
- Superior mesenteric vein basin: topography of jejunal and ileal branches
- Splenic vein basin and blood supply to the pancreas
- Structure of the rectal venous plexus
- Topography of vessels in the region of the porta hepatis and gallbladder
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