Portal System

Portal System Overview

• Definition: The portal system consists of blood vessels that direct blood from the gastrointestinal organs to the liver for detoxification before returning it to general circulation.

• Key Components:

  • Arteries: Carry oxygenated blood to tissues.

  • Veins: Carry deoxygenated blood back to the heart and lungs.

  • Portal Veins: Specifically transport blood from the gastrointestinal tract (stomach, intestines, pancreas) to the liver.

Portal Venous System Components

• Main Portal Vein (MPV):

  • Length: Approximately 7-8 cm.

  • Function: Carries nutrient-rich blood from the intestinal tract to the liver.

  • Branches: Splits into right and left portal veins within the liver.

  • Blood Flow Contribution: Supplies 75% of the liver's blood flow.

  • Normal Portal Venous Pressure: Ranges from 5-10 mmHg.

Formation of the Main Portal Vein (MPV)

• Location: Forms posterior to the neck of the pancreas.

• Junction: Created by the convergence of the superior mesenteric vein (SMV) and splenic vein (SV) at the "portal confluence".

• Pathway:

  • Courses posterior to the first part of the duodenum.

  • Flows into the porta hepatis (entrance of the liver) where it bifurcates into right and left portal branches.

• Inferior Mesenteric Vein (IMV): Drains into the splenic vein before the formation of the MPV.

Visualization of Portal Veins

• Portal veins can be easily visualized within the liver.

• Echogenicity: Their walls contain collagen, making them appear more echogenic compared to hepatic veins.

Review of Portal Venous System Vessels

• Vessels:

  • Inferior Mesenteric Vein (IMV)

  • Superior Mesenteric Vein (SMV)

  • Splenic Vein (SV)

  • Main Portal Vein (MPV)

  • Right Portal Vein (RPV)

  • Left Portal Vein (LPV)

Detailed Structure of Key Veins

• Splenic Vein:

  • Structure: A large, tortuous vessel arising from several tributaries at the hilus of the spleen.

  • Function: Drains blood from the stomach, spleen, and pancreas.

  • Formation: Joins with SMV to form the MPV.

• Superior Mesenteric Vein:

  • Function: Joins with the splenic vein to form the MPV.

• Inferior Mesenteric Vein:

  • Location: Drains into the splenic vein.

Imaging Characteristics

• Transverse Images: Visualize the MPV entering the liver, with LPV dividing into medial and lateral branches and RPV dividing into anterior and posterior segmental branches.

• Oblique Views in RUQ: Display gallbladder, right portal vein, hepatic vein, and inferior vena cava (IVC).

Normal Architecture Relationships

• Common Bile Duct (CBD): Relationship with the portal vein (PV) and hepatic artery (HA) is indicative of normal architecture.