Chylomicrons enter the bloodstream through which vessel?

• A. Portal vein
• B. Thoracic duct
• C. Aorta
• D. Inferior vena cava

Answer: (B)

Chylomicrons are large lipoprotein particles formed in intestinal cells from dietary fats, and they travel through the lymphatic system rather than directly into portal blood. Because they’re too large to enter the portal vein, they move into the intestinal lymphatics (lacteals) and ride along the lymphatic circulation, eventually reaching the thoracic duct. The thoracic duct drains into the bloodstream at the junction of the left subclavian and internal jugular veins, so chylomicrons enter the systemic circulation through the thoracic duct.

That’s why the portal vein isn’t the route for chylomicrons—the portal system carries nutrients straight to the liver, while chylomicrons bypass it initially. The aorta and inferior vena cava aren’t entry points for chylomicrons either; they don’t drain the lymphatic contents directly from the gut.