Hepatocyte

Information about Hepatocyte

Sinusoid of a rat liver with fenestrated endothelial cells. Fenestrae are approx 100 nm diameter, and the sinusoidal width 5 µm. Scanning electron micrograph by Robin Fraser, University of Otago.

Human liver

Hepatocytes make up 70-80% of the cytoplasmic mass of the liver. These cells are involved in protein synthesis, protein storage and transformation of carbohydrates, synthesis of cholesterol, bile salts and phospholipids, and detoxification, modification and excretion of exogenous and endogenous substances. The hepatocyte also initiates the formation and secretion of bile.

Hepatocyte histology

Hepatocytes display an eosinophilic cytoplasm, reflecting numerous mitochondria, and basophilic stippling due to large amounts of rough endoplasmic reticulum and free ribosomes. Brown lipofuscin granules are also observed (with increasing age) together with irregular unstained areas of cytoplasm; these correspond to cytoplasmic glycogen and lipid stores removed during histological preparation. The average life span of the hepatocyte is 5 months; they are able to regenerate.

Hepatocyte nuclei are round with dispersed chromatin and prominent nucleoli. Anisokaryosis is common and reflects tetraploidy & polyploidy, a normal feature of over 50% of hepatocytes. Binucleate cells are also common. Hepatocytes are organised into plates separated by vascular channels (sinusoids), an arrangement supported by a reticulin (collagen type III) network. The hepatocyte plates are one cell thick in mammals and two cells thick in the chicken. Sinusoids display a discontinuous, fenestrated endothelial cell lining. The endothelial cells have no basement membrane and are separated from the hepatocytes by the space of Disse which drains lymph into the portal tract lymphatics. Kupffer cells are scattered between endothelial cells; they are part of the reticuloendothelial system and phagocytose spent erythrocytes. Stellate (Ito) cells store vitamin A and produce extracellular matrix and collagen; they are also distributed amongst endothelial cells but are difficult to visualise by light microscopy.

Hepatocytes are an important physiological example for evalutation of both biological and metabolic effects of xenobiotics. They do not proliferate in culture. Hepatocytes are intensely sensitive to damage during the cycles of cryopreservation including freezing and thawing. Even after the addition of classical cryoprotectants there is still damage done while being cryopreserved. ^[1]

Protein synthesis

The hepatocyte is a cell in the body that manufactures serum albumin, fibrinogen, and the prothrombin group of clotting factors. It is the main site for the synthesis of lipoproteins, ceruloplasmin, transferrin, complement and glycoproteins. Hepatocytes manufacture their own structural proteins and intracellular enzymes.

Synthesis of proteins is undertaken by the rough endoplasmic reticulum (RER), and both the rough and smooth endoplasmic reticulum (SER) are involved in secretion of the proteins formed. The endoplasmic reticulum (ER) is involved in conjugation of proteins to lipid and carbohydrate moieties synthesized by, or modified within, the hepatocytes.

Carbohydrate metabolism

The liver forms fatty acids from carbohydrates and synthesizes triglycerides from fatty acids and glycerol. Hepatocytes also synthesize apoproteins with which they then assemble and export lipoproteins (VLDL, HDL).

Lipid metabolism

The liver receives many lipids from the systemic circulation and metabolizes chylomicron remnants. It also synthesizes cholesterol from acetate and then further synthesizes bile salts. The liver is the sole site of formation of bile salts.

Detoxification

Hepatocytes have the ability to metabolize, detoxify, and inactivate exogenous compounds such as drugs and insecticides, and endogenous compounds such as steroids.

The drainage of the intestinal venous blood into the liver requires efficient detoxification of miscellaneous absorbed substances to maintain homeostasis and protect the body against ingested toxins.

One of the detoxifying functions of hepatocytes is to modify ammonia into urea for excretion.

Additional images

Schemic diagram of Biliary system

References

1. ^ Hamel et al; "Wheat Extracts as an Efficient Cryoprotective Agent for Primary Cultures of Rat Hepatocytes": published online 21 Aug 2006 in Wiley Interscience www.interscience.wiley.com. Department des sciences bogiques, Montreal University.

External links

Histology at BU 22101ooa - "Ultrastructure of the Cell: hepatocytes and sinusoids"
Hepatic Histology: Hepatocytes (Colorado State University

• • [ e] Anatomy of torso, digestive system: Digestive glands
Organs	Pancreas (Tail, Body, Head, Islets of Langerhans) • Gallbladder • Liver (Hepatocyte, Space of Disse, Kupffer cell, Liver sinusoid, Hepatic stellate cell, Hepatic lobule)
Ducts	Bile ducts: (Bile canaliculus, Common hepatic duct, Cystic duct, Common bile duct) • Pancreatic duct • Hepatopancreatic ampulla

Cytoplasm is a gelatinous, semi-transparent fluid that fills most cells. Eukaryotic cells contain a nucleus that is kept separate from the cytoplasm by a double membrane layer. The cytoplasm has three major elements; the cytosol, organelles and inclusions.
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liver is an organ present in vertebrates and some other animals. It plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, and detoxification.
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Protein synthesis is the creation of proteins using DNA and RNA. Biological and artificial methods for creation of proteins differ significantly.

For biological protein synthesis, see protein biosynthesis.
For artificial protein synthesis, see peptide synthesis.

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Cholesterol is a sterol (a combination steroid and alcohol), a lipid found in the cell membranes of all tissues, and is transported in the blood plasma of all animals. Because cholesterol is synthesized by all eukaryotes, trace amounts of cholesterol are also found in membranes of
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Bile acids are steroid acids found predominantly in the bile of mammals.

Production and distribution

They are produced in the liver by the oxidation of cholesterol, conjugated (with either the amino acid taurine or glycine, or a sulfate, or a glucuronide) and are stored in
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U indicates the uncharged hydrophobic portion of the molecule, highlighted in blue.]]

Phospholipids are a class of lipids, and a major component of all biological membranes, along with glycolipids, cholesterol and proteins.
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Bile (or gall) is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver of most vertebrates. In many species, it is stored in the gallbladder between meals and upon eating is discharged into the duodenum
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Main article: Eosin

Eosinophilic means "loves eosin", and refers to the staining of certain tissues, cells, or organelles after they been washed with eosin, a dye.
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Basophilic is a technical term used by histologists. It describes the microscopic appearance of cells and tissues, as seen down the microscope, after a histological section has been stained with a basic dye. The most common such dye is haematoxylin.
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A ribosome is a small, dense, functional structure found in most known cells that assemble proteins and polypeptides used in cell division. It catalyses the assembly of individual amino acids into polypeptide chains by reading messenger RNAs and binding amino acids that are
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Lipofuscin is the name given to finely granular yellow brown pigment granules composed of lipid-containing residues of lysosomal digestion. It is considered one of the aging or "wear and tear" pigments; found in the liver, kidney, heart muscle, adrenals, nerve cells, and ganglion
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Glycogen is a polysaccharide of glucose (Glc) which functions as the primary short term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by the brain, uterus, and the vagina.
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Lipids can be broadly defined as any fat-soluble (hydrophobic), naturally-occurring molecules. The term is more-specifically used to refer to fatty-acids and their derivatives (including tri-, di-, and monoglycerides and phospholipids) as well as other fat-soluble sterol-containing
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nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles]]

In cell biology, the nucleus (pl.
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Chromatin is the complex of DNA and protein that makes up chromosomes. It is found inside the nuclei of eukaryotic cells, and within the nucleoid in prokaryotes.^[1] The nucleic acids are in the form of double-stranded DNA (a double helix).
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nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles]]

In cell biology, the nucleolus (plural nucleoli
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Polyploidy is the condition of some biological cells and organisms manifested by the presence of more than two homologous sets of chromosomes. Polyploid types are termed according to the number of chromosome sets in the nucleus: triploid (three sets; 3x),
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liver sinusoid is a type of sinusoidal blood vessel that serve as a location for the oxygen-rich blood from the hepatic artery and the nutrient-rich blood from the portal vein.
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endothelium is the thin layer of cells that line the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. Endothelial cells line the entire circulatory system, from the heart to the smallest capillary.
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basement membrane is a structure that supports overlying epithelial or endothelial cells.

Composition

The basement membrane consists of an electron-dense membrane called the lamina densa, about 30–70 nanometers in thickness, and an underlying network of reticular
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The lymphatic system is a complex network of lymphoid organs, lymph nodes, lymph ducts, lymphatic tissues, lymph capillaries and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system.
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The reticuloendothelial system (RES), part of the immune system, consists of the phagocytic cells located in reticular connective tissue, primarily monocytes and macrophages. These cells accumulate in lymph nodes and the spleen.
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Red blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen from the lungs or gills to body tissues via the blood.
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Vitamin A is an essential human nutrient. It exists not as a single compound, but in several forms. In foods of animal origin, the major form of vitamin A is an alcohol (retinol), but can also exist as an aldehyde (retinal), or as an acid (retinoic acid).
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extracellular matrix (ECM) is the extracellular part of animal tissue that usually provides structural support to the cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.
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Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, ^[1] making up about 25% of the total protein content.

Uses