Liver or Hepatic Acinus: It is the most preferred structural and functional unit of the liver now days. In cross section, it is a diamond-shaped or elliptical subdivision of liver parenchyma. It comprises parts of two adjacent hepatic lobules; the narrower ends of diamond are formed by two central veins, while the central wider part is formed by two portal triads (vascular core). The hepatic acinus is commonly divided into three zones (table 10.12).
Zone I is formed by the central part of liver acinus, which is present at the junction of adjacent sides, or peripheral parts of two hexagonal hepatic lobules. It receives best of the nutritive and oxygenated blood (through hepatic artery and portal vein), so hepatocytes of zone I are more liable to metabolic changes (like storage and depletion of glycogen). Similarly it is more liable to damage by toxins (eclampsia), phosphorous poisoning, chronic hepatitis and primary biliary cirrhosis.
Zone II is intermediate in position and less affected by the conditions producing changes in zones I and ill. However, it undergoes necrosis in yellow fever.
The peripheral zone (zone III) (hepatocytes of a liver acinus present nearer to central veins) receives less oxygenated and nutritive blood, so more liable to damage by hypoxia. It also undergoes necrosis in drug and chemical toxicity and right-sided cardiac failure.
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