Liver histology

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Liver histology

USMLE® Step 1 questions

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A researcher is studying the histology of liver parenchyma. Under histological examination, the liver parenchyma is divided into hexagonal hepatic lobules containing the central vein in the center and the portal triad at the periphery. Each hepatic lobule is divided into three different zones. The circled zone in the picture is most susceptible to which of the following injuries?  


The liver is the largest internal organ in the body and weighs about 1.5 kg.

It’s surrounded by a capsule of fibrous connective tissue called Glisson’s capsule.

If we look at the liver from an inferior view, which is a view from the bottom of the liver, we can see that the liver is divided into a large left lobe and right lobe, as well as two smaller lobes, called the quadrate and caudate lobes.

The liver parenchyma or functional tissue of the liver is organized into thousands of hepatic lobules, which have a dual blood supply that comes from terminal branches of the hepatic portal vein and hepatic artery.

The blood then flows through sinusoids surrounded by hepatocytes before draining into the lobule’s central vein.

Hepatocytes are the main functional cells of the liver that perform a large variety of functions, including the production of bile, a number of plasma proteins, and non-essential amino acids; the metabolism of fat, carbohydrate, and protein; the storage of glucose, vitamins, and iron; and the breakdown or detoxification of metabolic waste products, drugs, and toxins.

At lower magnification, the hexagonal shape of the hepatic lobules can be identified by their slightly darker edges and the prominent central veins in the center of each lobule.

The portal triad consists of a bile ductule, portal venule, and arteriole.

After identifying the lobule, it can be easier to locate portal triads in an image since they’re typically located at the corners of the lobules.

If we take a closer look at just one portal triad, we can more easily identify the portal venule by its large diameter and thin walls compared to the arteriole, which has a much smaller diameter and thicker walls.


The liver consists of thousands of hepatic lobules, which on microscopic examination are identified by their prominent central vein, as well as a slightly pale central portion of the lobule compared to the edges of the lobules. On corners of lobules lie portal triads, each containing a portal venule, hepatic arteriole, and bile duct. Venules can be identified by their large lumen and thin wall, as opposed to arterioles that have a thicker wall and a smaller diameter. The bile duct is identified by its simple cuboidal epithelium. The main cells of the liver parenchyma are hepatocytes. These are large polygonal cells with eosinophilic cytoplasm and basophilic nuclei.


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