The portal system is responsible for transporting blood from most of the gastrointestinal tract to the liver for metabolic processing before the blood returns to the heart. The portal system drains venous blood from the distal end of the esophagus, stomach, small and large intestines, proximal portion of the rectum, pancreas, and spleen. The portal system is the venous counterpart to areas supplied by the celiac trunk and the superior and inferior mesenteric arteries.
The portal venous system |
The liver is unique in that it receives both nutrient-rich deoxygenated blood (portal vein) and oxygenated blood (hepatic arteries). The portal vein branches as it enters the liver, where its blood percolates around hepatocytes in tiny vascular channels known as sinusoids. Hepatocytes detoxify the blood, metabolize fats, carbohydrates, and drugs, and produce bile. The sinusoids receive deoxygenated blood from the portal veins (provide blood for metabolism and detoxification) and oxygenated blood from the hepatic arteries (provide oxygen for hepatocytes). Blood exits the sinusoids into a central vein, which empties into the hepatic veins and ultimately into the inferior vena cava, which passes through the diaphragm before entering the right atrium of the heart.
Portal vein. |
Oral drugs travel throughout the gastrointestinal tract, where they are absorbed by the small intestine. These drugs then travel to the liver via the hepatic portal system, where they are metabolized before entering the systemic circulation.
📖 Sleisenger and Fordtran’s Gastrointestinal and Liver Disease- 2 Volume Set