A hepatocyte is a cell of the main tissue of the liver. Hepatocytes make up 80% of the liver's mass.
These cells are involved in:
-
Protein synthesis
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Storage protein
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Transformation of
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Synthesis of cholesterol, Bile acid and
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Detoxification, modification, and excretion of exogenous and endogenous substances
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Initiation of formation and secretion of bile
Structure
The typical hepatocyte is cubical with sides of 20–30
micrometre, (in comparison, a
human hair has a diameter of 17 to 180 μm).
[The diameter of human hair ranges from 17 to 181 μm. ] The typical volume of a hepatocyte is 3.4 x 10
−9 cm
3.
Smooth endoplasmic reticulum is abundant in hepatocytes, in contrast to most other cell types.
Microanatomy
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 cell nucleus are round with dispersed chromatin and prominent nucleoli. Anisokaryosis (or variation in the size of the nuclei) is common and often reflects tetraploidy and other degrees of polyploidy, a normal feature of 30–40% of hepatocytes in the adult human liver.
Hepatocytes are organised into plates separated by vascular channels (Liver sinusoid), an arrangement supported by a Reticular fiber (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.
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 microscope
Function
Protein synthesis
The hepatocyte is a cell in the
Human body that manufactures
serum albumin,
fibrinogen, and the
prothrombin group of
(except for Factors 3 and 4).
It is the main site for the synthesis of , ceruloplasmin, transferrin, complement, and .
Hepatocytes manufacture their own structural proteins and intracellular .
Synthesis of proteins is 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.
Proteins produced by hepatocytes that function as hormones are known as .
Carbohydrate metabolism
The
liver forms fatty acids from
and synthesizes triglycerides from fatty acids and glycerol.
Hepatocytes also synthesize
Apolipoprotein with which they then assemble and export lipoproteins (VLDL, 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.
Lipid metabolism
The liver receives many
from the systemic circulation and metabolizes
chylomicron remnants.
It also synthesizes
cholesterol from
acetate and further synthesizes
.
The liver is the sole site of bile salts formation.
Detoxification
Hepatocytes have the ability to metabolize, detoxify, and inactivate exogenous compounds such as
medication (see
drug metabolism),
, and endogenous compounds such as
.
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.
The most abundant organelle in liver cells is the smooth endoplasmic reticulum.
Aging
As mammalian liver cells age, damages in their DNA increase in prevalence. A review of the literature indicated that in mouse liver cells DNA damages (single-strand breaks, oxidized bases and 7-methylguanine) increase with age.
Also, in rat liver, DNA single- and double-strand breaks, oxidized bases, and methylated bases increase with age; and in rabbit liver, cross-linked bases increase with age.
[ Liver cells depend on DNA repair pathways that specifically protect the transcribed compartment of the genome to promote sustained functionality and cell preservation with age.]
Society and culture
Use in research
Primary hepatocytes are commonly used in cell biological and biopharmaceutical research. In vitro model systems based on hepatocytes have been of great help to better understand the role of hepatocytes in (patho)physiological processes of the liver. In addition, pharmaceutical industry has heavily relied on the use of hepatocytes in suspension or culture to explore mechanisms of drug metabolism and even predict in vivo drug metabolism.
For these purposes, hepatocytes are usually isolated from animal or human[ Erratum in: FASEB J 1989 May;3(7):1873.]
Additional images
File:Hepato-biliary.jpg|Schematic diagram of biliary system
File:Hepatocyte Culture.tif|Hepatocytes in cell culture
File:Membrane proteins of the polarized hepatocytes.jpg|Schematic of hepatocyte cell polarity, showing proteins localized to the basolateral and apical surfaces of the hepatocyte, referred to as the sinusoidal and canalicular membranes, respectively
See also
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List of human cell types derived from the germ layers
External links
