Hepatocytes: Definition, Structure, Micro Anatomy, Functions and Protein Synthesis

They are the most abundant type of cell in the human liver.

A hepatocyte is a cell of the main parenchymal tissue of the liver . Hepatocytes make up 70-85% of the liver mass. These cells are involved in:

  • Protein synthesis.
  • Protein storage.
  • Transformation of carbohydrates.
  • Synthesis of cholesterol, bile salts and phospholipids.
  • Detoxification, modification and excretion of exogenous and endogenous substances.
  • Start of bile formation and secretion.
  • Chemically process the molecules normally found in the body, such as hormones, as well as foreign substances such as medicines and alcohol.

Structure

The typical hepatocyte is cubic with sides of 20-30 μm, (in comparison, a human hair has a diameter of 17 to 180 μm). The typical volume of a hepatocyte is 3.4 x 10-9 cm3.

The smooth endoplasmic reticulum is abundant in the hepatocytes, while most of the cells in the body have small amounts.

Micro anatomy

The hepatocytes show an eosinophilic cytoplasm that reflects numerous mitochondria and dotted basophil due to large amounts of rough endoplasmic reticulum and free ribosomes.

Brown lipofuscin granules are also seen (as age increases) along with irregular areas of unstained cytoplasm; These correspond to glycogen and cytoplasmic lipid reserves during histological preparation.

The average life of the hepatocyte is 5 months; they are able to regenerate

The nuclei of the hepatocytes are round with scattered chromatin and prominent nucleoli.

Anicocariosis (or variation in the size of nuclei) is common and often reflects tetraploidy and other degrees of polyploidy, a normal feature of 30-40% of hepatocytes in adult human liver. Binucleated cells are also common.

The hepatocytes are organized in plates separated by vascular channels (sinusoids), an arrangement supported by a network of reticulin (collagen type III).

Hepatocyte plaques are one cell thick in mammals and two in chicken. The sinusoids show a discontinuous and fenestrated endothelial cell lining.

The endothelial cells do not have a basement membrane and are separated from the hepatocytes by the space of Disse, which drains the lymph into the lymphatic vessels of the portal tract.

The Kupffer cells are scattered between endothelial cells; they are part of the reticuloendothelial system and the erythrocytes consumed by phagocytosis.

Stellate (Ito) cells store vitamin A and produce extracellular matrix and collagen; They are also distributed among endothelial cells, but they are difficult to visualize by optical microscopy.

Functions

Protein synthesis: The hepatocyte is a cell in the body that makes serum albumin, fibrinogen and the group of prothrombin clotting factors (except factors 3 and 4).

It is the main site for the synthesis of lipoproteins, ceruloplasmin, transferrin, complement and glycoproteins. Hepatocytes make their own structural proteins and intracellular enzymes.

Protein synthesis is performed by the rough endoplasmic reticulum (RER), and both the rough and smooth endoplasmic reticulum (SER) participate in the secretion of the proteins formed.

The endoplasmic reticulum (ER) is involved in the conjugation of proteins with lipid and carbohydrate residues synthesized by, or modified within, hepatocytes.

Metabolism of carbohydrates: 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.

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 lipids from the systemic circulation and metabolizes the remains of chylomicrons. It also synthesizes acetate cholesterol and synthesizes bile salts even more. The liver is the only bile salt formation site.

Detoxification: Hepatocytes have the ability to metabolize, detoxify and inactivate exogenous compounds such as drugs (drug metabolism) and insecticides and endogenous compounds such as steroids.

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

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

The most abundant organelle in liver cells is the smooth endoplasmic reticulum.