Vàng da (Jaundice)

Mô tả: Vàng da, vàng mắt và niêm mạc.

Nguyên nhân: There are many different causes of jaundice; they can be grouped as shown in Table 6.5.

Cơ chế: Jaundice is caused by a build-up of excess bilirubin that is then deposited in the skin and mucous membranes. Jaundice is not clinically evident until bilirubin exceeds 3 mgL. Defects along the bilirubin pathway (shown in Figure 6.15) lead to increased bilirubin and jaundice. Pre-hepatic See ‘Haemolyticpre-hepatic jaundice’ in Chapter 4, ‘Haematologicaloncological signs’. Intrahepatic In intrahepatic jaundice the liver’s ability to take up bilirubin, bind, conjugate andor secrete it into the bile canaliculi is impaired. This can be due to either acquired damage to or necrosis of liver cells or genetic deficiencies in the bilirubin pathway. For example, in Gilbert’s syndrome, a genetic abnormality of the enzyme glucuronyltransferase reduces the ability to conjugate bilirubin. As a result, unconjugated bilirubin cannot be excreted properly and hyperbilirubinaemia occurs to a level that eventually causes jaundice. Similarly, in Dubin–Johnson syndrome a genetic defect in a transporter (cMOAT) does not allow conjugated bilirubin to be secreted effectively, and again bilirubin rises, resulting in jaundice. Post-hepatic Post-hepatic jaundice is caused by a blockage of bile ducts preventing the excretion of conjugated bilirubin. Bile backs up through the liver into the blood. Jaundice 471 Senescent erthrocytes Haem Heme oxygenase Mononuclear phagocytic cell Biliverdin reductase Biliverdin Bilirubin– albumin complex Bilirubin glucuronides Hepatocyte Liver Bile ducts Bile canaliculus Duodenum Urobilinogen Colon Blood