Hepatocytes

The hepatocytes are cells which comprise the liver parenchyma. They are its primary functional units. Each individual cell has the capacity for all functions. As a group, the hepatocytes perform a vast array of physiological tasks, all of which are necessary for the maintenance of biologic homeostasis.

In the normal adult liver, it has been estimated that there are about 250 billion hepatocytes (1:xxix). Indeed, the liver is the largest visceral organ in mammals; in man, its weight is approximately 1.5 kilograms (8:8).

The development of the liver parenchyma starts from entodermal cells. These embryonic precursors grow into the mesenchyma of the septum transversum (8:8). The organ itself generally performs two major actions. At one end of the spectrum, the liver serves an ingestive function. For example, it absorbs metabolites from the blood. In addition, the hepatocytes also have a secretory capacity. The liver produces a number of compounds which are secreted back into either the blood or the bile.

The hepatocytes comprise approximately 80% of a human liver's volume. Moreover, these cells make up about 60% of the organ's total cell number (8:10). In histological sections, these parenchymal cells appear irregularly polygonal and range in diameter from 18 to 30 microns (6:11). These similarlooking cells also tend to be joined laterally. Thus, they form complicated, walllike structures of anastomosing plates known as the hepatic muralium

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size classes which tend to occur according to specific ratios (8:11). In addition to the nuclei, a number of other hepatocyte organelles have also been quantitatively analyzed (1:xxix). For example, there are about 2,000 mitochondria per hepatocyte. These account for approximately 18% of the total cellular volume. In addition, about 7% of the cellular space is occupied by the rough endoplasmic reticulum, and 12% each cell consists of smooth endoplasmic reticulum and Golgi apparatus. The hepatocyte's plasma membrane consists of a 7 nanometer thick bilayer. This membrane has been found to contain a relatively high amount of glycosylated protein and lipids, as well as a high number of complex polypeptides (1:xxix). The liver's hepatocytes are interposed between the digestive tract and the rest of the body (9:255). These cells are responsible for processing high quantities of different compounds. Some of these include amino acids, carbohydrates, lipids, vitamins, and other materials (1:xxiii). Many of the substrates are ingested for subsequent storage or metabolism. For example, one function of hepatocytes is to store glycogen (2:14). The rate at which a substance is taken up by the liver and then metaboliz

Category: Medical - H