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Concept
Lobules of liver
Résumé
In histology (microscopic anatomy), the lobules of liver, or hepatic lobules, are small divisions of the liver defined at the microscopic scale. The hepatic lobule is a building block of the liver tissue, consisting of a portal triad, hepatocytes arranged in linear cords between a capillary network, and a central vein.
Lobules are different from the lobes of liver: they are the smaller divisions of the lobes. The two-dimensional microarchitecture of the liver can be viewed from different perspectives:
The term "hepatic lobule", without qualification, typically refers to the classical lobule.
The hepatic lobule can be described in terms of metabolic "zones", describing the hepatic acinus (terminal acinus). Each zone is centered on the line connecting two portal triads and extends outwards to the two adjacent central veins. The periportal zone I is nearest to the entering vascular supply and receives the most oxygenated blood, making it least sensitive to ischemic injury while making it very susceptible to viral hepatitis. Conversely, the centrilobular zone III has the poorest oxygenation, and will be most affected during a time of ischemia.
A portal triad (also known as portal canal, portal field, portal area, or portal tract) is a distinctive arrangement within lobules. It consists of the following five structures:
proper hepatic artery, an arteriole branch of the hepatic artery that supplies oxygen
hepatic portal vein, a venule branch of the portal vein, with blood rich in nutrients but low in oxygen
one or two small bile ductules of cuboidal epithelium, branches of the bile conducting system.
lymphatic vessels
branch of the vagus nerve
The misnomer "portal triad" traditionally has included only the first three structures, and was named before lymphatic vessels were discovered in the structure. It can refer both to the largest branch of each of these vessels running inside the hepatoduodenal ligament, and to the smaller branches of these vessels inside the liver.
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