As the name suggests, hepatocytes are specific cells present in the liver. The term "hepato-" denotes "related to the liver", while the word "-cyte" refers to a cell. Hepatocytes are among the most multi-tasking cells found in our body as they play a variety of vital roles that are associated with the functioning of the liver. These cells are actually a type of epithelial tissue, which not only lines, but also covers our entire body right from our nose to the toes. On the other hand, nearly all tumours related to the liver develop in hepatocytes, for instance hepatocellular carcinoma.
Something like 60 percent to 80 percent of the liver's mass is always composed of hepatocytes. These specialized cells are shaped like a polygonal plate and are heaped on top of one another in layers. When they come in contact with nearby cells, it makes it easier for hepatocytes to perform certain specific functions. Aside from their natural habitat, which is the liver, for research purpose it is also possible to grow hepatocytes in culture. When grown in culture, these cells develop into elongated chains and layers, connecting with one another. The cells grown in laboratories are from various different species and they are provided in fresh as well as frozen varieties with a view to fulfill different requirements for various types of researches.
Hepatocytes have a number of functions and synthesis of protein and its storage is among their vital functions. These specialized liver cells produce as well as store an assortment of proteins which are used by our body. Moreover, hepatocytes also work to break down carbohydrates and lipids from the ingested foods. Their functions also include producing and secreting bile, which is released from the liver through the bile duct. Liver plays a vital role in our digestive process.
Aside from these, hepatocytes also perform various other functions in our body. In fact, these cells serve as the filtration system of our body. They process several compounds consumed by people and metabolize them, transforming these compounds into simpler elements that can be used by our body, while excreting the wastes produced during the process. As far as the liver is concerned, the hepatocytes are meant to enmesh and deactivate the toxins even before they are able to enter the remaining body areas and harm them. Such toxins also include those that people consume willingly and they may vary from pharmaceutical compounds to recreational drugs. Some pharmaceutical drugs we take to cure ailments may contain toxins and these are neutralized by the hepatocytes.
Similar to other cells in our body, even hepatocytes can become carcinogenic. In case the liver is damaged, it can regrow and, in such cases, the hepatocytes are stimulated to work overtime. A single cell with rogue DNA that can successfully elude the system of the body to spot and destroy the damaged cells has the ability to reproduce, thereby resulting in the growth of a mass inside the liver. After a while, this mass will weaken the functioning of the liver and sooner or later may even result in the failure of this vital organ to function. People who have been suffering from liver scarring, also referred to as cirrhosis, are more vulnerable to suffer from liver cancer.
Hepatocytes are involved in various functions. Some of them include synthesis and storage of proteins; metabolizing carbohydrates; cholesterol, phospholipids and bile salt as well as bile formation and its secretion. In addition, these specialized liver cells are also engaged in modification, detoxification and excretion of both exogenous as well as endogenous substances.
Hepatocytes can also detoxify, metabolize and render exogenous compounds like drugs inactive - a process known as drug metabolism. They also possess the ability to break down, detoxify and inactivate insecticides and various endogenous compounds, including steroids.
Sometimes venous blood drains from the intestine into the liver and it is necessary to detoxify this blood efficiently in order to maintain homeostatis by absorbing various miscellaneous substances. This is also required to protect our body from assorted toxins that we often ingest voluntarily.
One major detoxifying utility of these specialized liver cells is to transform ammonia into urea so that it can be excreted. The smooth endoplasmic reticulum is known to be the organelle that is found in abundance in the liver cells.
Hepatocytes, also known as the liver's epithelial cells, develop into spreading cell plates, generally just one cell thick, found between the capillary sinusoids system, which links the portal tracks with the central vein.
The hepatocytes are in direct contact with the blood that circulates through the liver and this makes it easier for exchanging various substances between these specialized cells and the blood. In fact, these cells and the blood sinusoids in the liver are in very close contact. These sinusoids transport blood from the lobule's edge to the central vein.
Two different types of cells - known as Kupffer cells and phagocytic cells, line the sinusoids. On the other hand, sinusoid lining cells are akin to the endothelial cells that form the lining of the other blood vessels.
Blood goes into the liver via portal tracts found on the external periphery of the liver lobule and is purified while passing through the sinusoids. These sinusoids are closely connected to the hepatocytes in the liver until the blood is carried to the central hepatic vein. In the central hepatic vein, the blood seeps away. In this way, the blood moves from the outside of the liver lobule to its internal areas.
On the contrary, bile secreted through the bile duct passes through a canaliculi (small passages or canals), which are formed by hepatocytes. Bile passes through these canaliculi from the liver lobules inside to outside.
All the while the discussion was focused on the hepatocytes, so one may wonder what Kupffer cells are. In fact, these are specific types of immune cells that are only found inside the liver. Kupffer cells are among the many types of macrophages, a form of leukocytes (white blood cells), which facilities the body to remain healthy by killing bacteria, destroying old blood cells and various alien substances that often crop up in the blood stream due to injuries, ailments or malfunctioning of the body. These macrophages may also occur when the various body cells age naturally. Kupffer cells grow inside the bone marrow and subsequently travel to the liver. Inside the liver, these cells become completely developed and form specialized cells that are meant to shield the liver from any kind of harm or damage.
Karl Wilhelm von Kupffer, a German anatomist, is credited with discovering these macrophages in 1876 and, hence, their name. Initially, it was believed that Kupffer cells had their origin inside the liver and they were a part of the lining of the blood vessels found in the liver. Further studies as well as observation by a Polish scientist named Tadeusz Browicz made him realize that these macrophages did not originate in the liver, but were formed inside the bone marrow. He discovered this in 1898; just two decades after Kupffer originally discovered these cells. Kupffer cells are also referred to as Browicz-Kupffer cells owing to the discovery and identification of their functions by the Polish scientist. Following this, many scientists studied these cells and unveiled their several different functions. Now, it has been established that Browicz-Kupffer cells have an important role in the dead blood cell recycling as well as assisting the liver to react to the toxic materials present in the blood stream.
Since Kupffer cells also have normal immune functions, they also aid in repairing any kind of harm to the liver. They are also involved in the development of liver cirrhosis, a grave ailment distinguished by excessive fibrous tissues and scarring of this vital organ. In most cases, liver cirrhosis is attributed to too much alcohol consumption. Aside from this, a number of stimulators like carcinogenic agents may also result in these cells producing the connective tissue called collagen inside the liver itself. When there is an excess of collagen and too much scarring inside the liver, they make the liver ineffective. Sooner or later, they make the liver incapable of undertaking its usual functions. At the same time, unlike in normal circumstances, presence of excessive collagen and too much scarring inside the liver makes it very difficult for the liver to reinforce itself.