Learning Objectives

• Distinguish between the Systemic (IVC) and Portal venous systems.
• Trace the formation of the Inferior Vena Cava at L5 and its exit at T8.
• Identify the tributaries of the Portal Vein and its role in nutrient processing.
• Master the four major Porto-Systemic Anastomoses and their clinical significance in portal hypertension.

The Systemic System: Inferior Vena Cava (IVC)

The IVC is the largest vein in the body, returning deoxygenated blood from everything below the diaphragm to the Right Atrium.

• Formation: Union of the Common Iliac Veins at the L5 level.
• Course: Ascends to the right of the aorta, piercing the diaphragm’s central tendon at the T8 level (Caval Hiatus).
• Asymmetric Tributaries (High-Yield):
  • The Right Gonadal and Suprarenal veins drain directly into the IVC.
  • The Left Gonadal and Suprarenal veins drain into the Left Renal Vein first.

The Portal Venous System

This system directs nutrient-rich blood from the GI tract and spleen to the liver for detoxification and processing before it reaches the systemic circulation.

• Formation: Union of the Splenic Vein and Superior Mesenteric Vein (SMV) posterior to the neck of the pancreas at the L2 level.
• Tributaries:
  • Splenic Vein: Receives the Inferior Mesenteric Vein (IMV), short gastrics, and pancreatic veins.
  • SMV: Drains the midgut (small intestine to 2/3 transverse colon).
  • Portal Vein Proper: Receives the Gastric veins (stomach) and Cystic veins (gallbladder).

Porto-Systemic Anastomoses & Portal Hypertension

When liver flow is blocked (e.g., Cirrhosis), portal pressure rises (> 20 mmHg), forcing blood into “backup” systemic routes. These veins dilate, forming Varices.

Clinical Summary

• Oesophageal Varices: These are the most dangerous. Rupture leads to massive, often fatal upper GI bleeding.
• Left Renal Vein Entrapment: Since the left gonadal vein drains here, compression (Nutcracker Syndrome) can cause a left-sided varicocele.

Activity