Hepatocytes

The Hepatocytes are the real ones Liver cellsthat make up over 80 percent of the liver. They are responsible for most of the metabolic processes such as the synthesis of proteins and active substances, the breakdown of metabolic products and the detoxification reactions. Disturbances in the function of the hepatocytes can lead to central metabolic diseases and symptoms of intoxication.

What are the hepatocytes?

With over 80 percent, the hepatocytes represent the largest part of the liver cells and form the so-called liver parenchyma. The most important functions of the liver are connected to the liver parenchyma. The hepatocytes are very large cells with a diameter of 30-40 micrometers. They also have a large core and sometimes contain two cores. Their set of chromosomes is usually diploid. However, hepatocytes can also have a polyploid set of chromosomes.

Very intensive metabolic processes take place within the hepatocytes, which are controlled by a large number of cell organelles. They very rarely share. They are formed mainly from pluripotent stem cells in the transition area between liver tissue and the outgoing biliary tract. There the stem cells transform into both hepatocytes and cholangiocytes. Hepatocytes are also in direct contact with the blood plasma via the basolateral membranes.

Anatomy & structure

The hepatocytes are very large cells with large cell nuclei and numerous cell organelles that ensure very intensive metabolic activity. The hepatocyte has a strongly polarized structure and function. Basolateral (sinusoidal) and apical (canalicular) membranes are present. At the same time, the basal lamina is missing. The apical membranes are responsible for the secretion of bile by the numerous microvilli.

The basolateral membranes border a sinusoid through microvilli so that substances can be exchanged between the blood and the hepatocyte. The hepatocytes have a number of cell organelles to carry out their numerous metabolic functions. First of all, they contain large diploid or polyploid cell nuclei. There are also many mitochondria, peroxisomes and lysosomes.

Individual lipid droplets and glycogen fields are stored in the hepatocytes as storage substances. The concentration of glycogen depends on the nutritional status and changes several times during the day. A strongly developed endoplasmic reticulum and a strong Golgi apparatus testify to the high metabolic activity of the liver cells. Certain active substances are secreted through numerous secretory vesicles. After all, a well-developed cytoskeleton maintains the shape of the hepatocytes.

Function & tasks

Hepatocytes play a central role in the body's metabolic processes. They are responsible for providing transport proteins for hormones, fats, vitamins or foreign substances. They provide albumins as transport proteins and amino acids, fats and glucose for energy production. The breakdown of metabolic products also takes place via the hepatocytes.

The same applies to the detoxification of foreign substances and the excretion of their breakdown products via the kidneys and bile. Another important function of the hepatocytes is the formation of bile. With the help of bile, cholesterol, bile acids, bilirubin and the breakdown products of toxic foreign substances can be excreted. The acid-base balance is also regulated by the hepatocytes. Most of the metabolic functions are controlled in the cell organelles. In the cytosol, for example, the storage, synthesis and breakdown of glucogen take place. Glucose is also produced there from amino acids by means of so-called gluconeogenesis.

Part of the heme synthesis also takes place in the cytosol of the hepatocytes. In the mitochondria of the hepatocytes, part of the heme synthesis, the gluconeogenesis and part of the urea cycle and urea synthesis also take place. In addition, toxic substances including drugs are broken down there via the cytochrome P450 system. The synthesis of bile acids and cholesterol takes place in the smooth endoplasmic reticulum and in the Golgi apparatus of the hepatocytes.

In addition, heme is broken down into bilirubin there. In the rough endoplasmic reticulum, albumin, transport proteins, coagulation factors and apoliproteins are synthesized. The same reactions do not take place in all hepatocytes. The intensity of the individual metabolic processes depends on the position of the corresponding liver cell in relation to the blood vessel system. The metabolic functions within the liver parenchyma are divided into three zones. Zone 1 represents the area where the portal blood enters the liver tissue. In zone 3, the blood collects from the liver tissue to the central veins leading away. Zone 2 lies in between.

Diseases

There are liver diseases that mainly affect the hepatocytes. In other liver disorders, they are not involved at all. Liver diseases in which the hepatocytes are exclusively involved include inflammation of the liver (hepatitis), fatty liver disease, toxic damage to the liver, allergic-hyperergic mechanisms or congenital storage diseases. Liver inflammation can have various causes. Several forms of virus hepatidis are known. Autoimmunological liver inflammation also occurs.

Liver inflammation leads to the death of liver parenchyma. Since the liver tissue is very capable of regeneration, the hepatocytes are replaced again after the disease has been overcome. With a chronic course, however, the liver tissue can become scarred with the development of liver cirrhosis. The detoxification capacity of the liver decreases more and more. In the final stage there is general organ failure through poisoning of the body.

But also severe acute and chronic poisoning can lead to the breakdown of liver tissue with the formation of liver cirrhosis. A typical acute poisoning is caused, for example, by consuming the green leaf mushroom. If the patient survives, cirrhosis of the liver develops. Chronic poisoning is caused, among other things, by the regular consumption of alcohol and drug abuse. Here, too, the detoxification capacity of the hepatocytes is overwhelmed in the long term, so that severe liver damage develops.