Sinusoid of a rat liver with fenestrated endothelial cells. Rats are various medium sized long-tailed Rodents of the superfamily Muroidea Fenestrae are approx 100 nm diameter, and the sinusoidal width 5 µm. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre Scanning electron micrograph by Robin Fraser, University of Otago. The University of Otago ( Te Whare Wānanga o Otāgo) in Dunedin is New Zealand 's oldest university with over 20000 students enrolled during

Human liver

Hepatocytes make up 70-80% of the cytoplasmic mass of the liver. The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. The liver is a vital organ in the human body and is present in Vertebrates and some other animals 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. Protein synthesis is the creation of proteins using DNA and' RNA'. Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian Bile acids (also known as bile salts are Steroid Acids found predominantly in the Bile of Mammals. Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate The hepatocyte also initiates the formation and secretion of bile. Bile or gall is a bitter yellow or green Alkaline fluid secreted by Hepatocytes from the Liver of most Vertebrates In many species

Hepatocyte histology

Hepatocytes display an eosinophilic cytoplasm, reflecting numerous mitochondria, and basophilic stippling due to large amounts of rough endoplasmic reticulum and free ribosomes. See also Eosin Eosinophilic means loves eosin, and refers to the Staining of certain tissues, cells, or Organelles In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Basophilic is a technical term used by histologists. It describes the microscopic appearance of cells and tissues as seen down the Microscope, The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that 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. Lipofuscin is the name given to finely granular yellow brown Pigment granules composed of Lipid -containing residues of Lysosomal digestion Glycogen is a Polysaccharide of Glucose (Glc which functions as the secondary short term energy storage in Animal cells Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble 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. In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed Chromatin is the complex basis of DNA and protein that makes up Chromosomes It is found inside the nuclei of eukaryotic cells, and within the The nucleolus (also called nucleole) is a structure found within the nucleus in which Ribosomal RNA is transcribed. Anisokaryosis is common and reflects tetraploidy & polyploidy, a normal feature of over 50% of hepatocytes. Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes. Polyploidy occurs in cells and Organisms when there are more than two homologous sets of Chromosomes. 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. A liver sinusoid is a type of sinusoidal blood vessel (with fenestrated discontinuous endothelium that serve as a location for the oxygen-rich blood from the Hepatic artery 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 endothelium is the thin layer of cells that line the interior surface of Blood vessels forming an interface between circulating Blood in the 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. The basement membrane is a structure that supports overlying Epithelial or Endothelial cells. The lymphatic system in Vertebrates is a network of conduits that carry a clear fluid called Lymph. The lymphatic system in Vertebrates is a network of conduits that carry a clear fluid called Lymph. Kupffer cells are scattered between endothelial cells; they are part of the reticuloendothelial system and phagocytose spent erythrocytes. The reticuloendothelial system ( RES) part of the Immune system, consists of the phagocytic cells located in Reticular connective tissue, primarily Red blood cells are the most common type of Blood cell and the Vertebrate body's principal means of delivering Oxygen to the body tissues via the Blood 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. Vitamin A refers to a family of similarly shaped molecules the Retinoids. In Biology, the extracellular matrix ( ECM) is the Extracellular part of animal tissue that usually provides structural support to the cells Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein

Hepatocytes are an important physiological example for evalutation of both biological and metabolic effects of xenobiotics. A xenobiotic is a Chemical which is found in an Organism but which is not normally produced or expected to be present in it 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. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called With regard to living things, a body is the integral physical material of an individual Serum albumin, often referred to simply as albumin, is the most abundant Plasma protein in humans and other Mammals Albumin is essential for maintaining Fibrin (also called Factor Ia) is a Protein involved in the clotting of blood Thrombin (activated Factor II ') is a Coagulation protein that has many effects in the coagulation cascade. Coagulation is a complex process by which Blood forms Clots It is an important part of Hemostasis (the cessation of blood loss from a damaged vessel whereby It is the main site for the synthesis of lipoproteins, ceruloplasmin, transferrin, complement and glycoproteins. A lipoprotein is a biochemical assembly that contains both Proteins and Lipids The lipids or their derivatives may be covalently or non-covalently bound Ceruloplasmin (or caeruloplasmin) is officially known as ferroxidase or iron(IIoxygen oxidoreductase. Transferrin is a Blood plasma Protein for Iron Ion delivery Transferrin is a Glycoprotein, which binds iron very tightly but reversibly The complement system is a Biochemical cascade that helps clear Pathogens from an organism Not to be confused with Peptidoglycan. Glycoproteins are proteins that contain Oligosaccharide chains ( Glycans) covalently attached Hepatocytes manufacture their own structural proteins and intracellular enzymes. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins

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 (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle The endoplasmic reticulum (ER) is involved in conjugation of proteins to lipid and carbohydrate moieties synthesized by, or modified within, the hepatocytes. The endoplasmic reticulum (Greek endo = "within" (prefix plásma = "formed entity" Latin reticulum = "little net" or ER, is an Organelle

Carbohydrate metabolism

See also: Lipogenesis

The liver forms fatty acids from carbohydrates and synthesizes triglycerides from fatty acids and glycerol. Lipogenesis is the process by which simple sugars such as Glucose are converted to Fatty acids which are subsequently esterified with Glycerol The liver is a vital organ in the human body and is present in Vertebrates and some other animals Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most Hepatocytes also synthesize apoproteins with which they then assemble and export lipoproteins (VLDL, HDL). High-density lipoproteins ( HDL) is one of the 5 major groups of Lipoproteins ( Chylomicrons, VLDL, IDL, LDL, HDL

The liver is also the main site in the body for gluconeogenesis, the formation of carbohydrates from precursors such as alanine, glycerol and oxaloacetate. Gluconeogenesis (abreviated GNG) is a Metabolic pathway that results in the generation of Glucose from non- Carbohydrate carbon substrates such Alanine (abbreviated as Ala or A) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH3 Oxaloacetic acid is an Organic compound with the chemical formula HO2CC(OCH2CO2H

Lipid metabolism

The liver receives many lipids from the systemic circulation and metabolizes chylomicron remnants. Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble Chylomicrons are large lipoprotein particles that transport dietary lipids from the intestines to other locations in the body It also synthesizes cholesterol from acetate and then further synthesizes bile salts. Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian An acetate, or ethanoate, is either a salt or Ester of Acetic acid. Bile acids (also known as bile salts are Steroid Acids found predominantly in the Bile of Mammals. 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. Medication, also referred to as medicine, can be loosely defined as any substance intended for use in the diagnosis cure mitigation treatment or prevention of disease An insecticide is a Pesticide used against Insects in all developmental forms A steroid is a Terpenoid Lipid characterized by a Carbon skeleton with four fused rings generally arranged in a 6-6-6-5 fashion

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. In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists In the Circulatory system, a vein is a Blood vessel that carries Blood back toward the Heart (as opposed to Artery, a blood vessel Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products The liver is a vital organ in the human body and is present in Vertebrates and some other animals Homeostasis (from Greek: ὅμος hómos, "equal" and ιστημι istēmi, "to stand" lit

One of the detoxifying functions of hepatocytes is to modify ammonia into urea for excretion. Urea is an Organic compound with the Chemical formula ( N[[hydrogen H]]22 C[[oxygen O]]

Additional images

Schemic diagram of Biliary system

References

External links

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