Hepatitis | Organ & infection

Background information

The liver is one of our most important organs and the immune system of our body is a fascinating system. Would you like to learn more about both?

In this chapter you will find short descriptions and first key words to give you an overview and more insights into these subjects.

  • What are the functions of the liver?
  • What are the possible causes for liver diseases?
  • What are the different forms of viral hepatitis and what is the structure of the hepatitis virus?
  • How do hepatitis viruses proliferate?
  • How does the human body respond to the viruses?

The liver

The organ at a glance

name greek: hepar
status most essential organ for metabolism and detoxification in humans
location upper right quadrant of the abdomen, below the diaphragm
size largest organ in humans
weight 1.500 – 2.000 g, ca. 4 % of body weight
composition right hepatic lobe, left hepatic lobe
requirements 28 % of the blood flow, 20 % of the total body oxygen
sensation of pain - inner part of the organ is unsusceptible to pain
- organ capsule is susceptible to pain, e.g. due to tension caused by organ enlargement
functions - utilization of amino acids and proteins
- conversion of sugar molecules into starch (energy storage)
- production of energy out of fats
- conversion of fats for storage
- storage of starch and proteins
- storage of vitamins (B12 and A) and trace elements
- activation and degradation of hormones
- degradation of toxins and drugs
products - blood clotting factors
- enzymes
- hormones
- bile juice (ca. 600 ml/p.d.)
system partners - blood vessels
- arteries
- portal vein
- gall bladder
- bile ducts
- intestine
- heart
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Hepatitis

Hepatitis and its potential causes

The inflammation of the liver (= hepatitis) is a defence reaction of the immune system.

This reaction can be caused by:

  • pathogens (viruses, bacteria, parasites)
  • xenobiotics
  • metabolic diseases
  • autoimmune diseases
  • pregnancy

Viruses causing hepatic inflammation are:

  • hepatitis viruses > inflammation of the liver
  • cytomegalia virus
  • Epstein-Barr virus > Pfeiffer's disease
  • varicella-zoster virus > chickenpox, shingles
  • herpes-simplex virus
  • yellow fever virus

For many of the above mentioned viruses the inflammation of the liver is just one possible affection of the body. Only the hepatitis viruses affect primarily the liver.

The yellow fever virus also affects the liver. Infections with this virus have a high mortality rate. It is found mainly in tropical and subtropical regions in South America and Africa. A vaccination is recommended for travellers to those regions.

Other causes of hepatitis can be special bacteria and parasites.

Bacteria

  • leptospires
  • brucella


Parasites

  • amoeba

Xenobiotics play an important role in cases of hepatitis, such as

  • medicine
  • alcohol
  • drugs
  • toxic substances
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Hepatitis virus

There are different types of viral hepatitis due to different types of hepatitis viruses. They belong to different viral families not related to each other.

Hepatitis viruses Hepatitis A virus (HAV) Hepatitis B virus (HBV) Hepatitis C virus (HCV) Hepatitis D virus (HDV) Hepatitis E virus (HEV)
Size 42 nm 45 nm
Genetic information RNA DNA RNA RNA RNA

Composition of the hepatitis virus

The hepatitis virus is composed of the following main elements:

  • genetic information (see above)
  • proteins
  • Lipid envelope taken from the host cell

As the virus has no innate metabolism, it uses the human cell as host cell for replication.

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Viral proliferation

The hepatitis viruses replicate in the human body by

  • binding to a liver cell (hepatocyte)
  • entering the cell
  • release of viral DNA (B) or RNA (A,C,D, E,F,G)
  • "re-programming" of the cell
  • integration into the human genome ("hepatitis B" virus)
  • production of new viral particles
  • leaving the host cell as a complete virus
  • affection of other hepatocytes
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The immune response

The reaction of the body against viral infections is very complex. As an early response the body produces interferons. Interferons are proteins that act as messengers in the body and play a prominent role in the defense against viruses.

Interferons have the following functions:

  • they inhibit cell growth and
  • activate the immune system

The immune system

  • produces white blood cells such as natural killer cells, antibody producing lymphocytes and lymphocytes regulating the immune system
  • destroys cells infected with viruses by an interaction of antibodies, macrophages and lymphocytes
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