from SECTION I - PATHOPHYSIOLOGY OF PEDIATRIC LIVER DISEASE
Published online by Cambridge University Press: 18 December 2009
A portal system is one, which by definition, begins and ends with capillaries. The major portal system in humans is one in which the capillaries originate in the mesentery of the intestines and spleen and end in the hepatic sinusoids. Capillaries of the superior mesenteric and splenic veins supply the portal vein with a nutrient- and hormone-rich blood supply (Figure 7.1). The partially oxygenated portal venous blood supplements the oxygenated hepatic arterial flow to give the liver unique protection against hypoxia. Blood flow from the hepatic artery and portal vein is well coordinated to maintain consistent flow and explains the ability of the liver to withstand thrombosis of either of these major vascular structures. This well-regulated blood flow in conjunction with the very low resistance found in the portal system results in a low baseline portal pressure in healthy individuals.
Portal hypertension, defined as an elevation of portal blood pressure above 5 mm Hg, is one of the major causes of morbidity and mortality in children with liver disease (Table 7.1). The high prevalence of biliary tract disease in pediatric liver disorders (e.g., biliary atresia), as compared with adult liver disorders, predisposes to the expression of portal hypertension earlier in the clinical course of liver disease relative to the manifestation of the sequelae of hepatic insufficiency. Portal hypertension is a complication of a wide variety of pediatric liver disorders (Table 7.1). Its complications are some of the leading indications for liver transplantation.
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