The liver is the largest organ in the body,
occupying the entire upper right quadrant of the abdomen. It performs over
500 vital functions. It processes all of the nutrients the body requires,
including proteins, glucose, vitamins, and fats. The liver manufactures
bile, the greenish fluid stored in the gall bladder that helps digest fats.
One of the liver's major contributions to life is to render harmless
potentially toxic substances, including alcohol, ammonia, nicotine, drugs,
and harmful by-products of digestion. Old red blood cells are removed from
the blood by the liver and spleen, and the iron is cycled to the bone marrow
to make new ones. Damage to the liver can impair these and many other
processes. Hepatitis is a disorder in which viruses or other mechanisms
produce inflammation in liver cells, resulting in their injury or
destruction. In most cases this inflammatory process is triggered when the
immune system fights off infections caused by viruses. It can also be
caused, however, by an overactive immune system that attacks its own liver
cells. Inflammation of the liver can also occur from medical problems,
drugs, alcoholism, chemicals, and environmental toxins. Hepatitis varies in
severity from a self-limited condition with total recovery to a
life-threatening or life-long disease.
Experts define hepatitis as
short-term (acute hepatitis) or prolonged (chronic hepatitis). In some
cases, acute hepatitis develops into a chronic condition, but chronic
hepatitis can also occur on its own. Although chronic hepatitis is generally
the more serious condition, patients having either condition can experience
varying degrees of severity.
Acute hepatitis can begin suddenly or
gradually, but it has a limited course and rarely lasts beyond one or two
months. Usually there are only spotty liver cell damage and evidence of
immune system activity, but on rare occasions, acute hepatitis can cause
severe -- even life-threatening -- liver damage.
The chronic forms of hepatitis persist for
prolonged periods. Experts usually categorize chronic hepatitis as either
(1) chronic persistent or (2) chronic active hepatitis.
Chronic Persistent Hepatitis
Chronic persistent hepatitis is usually
mild and nonprogressive or slowly progressive, causing limited damage to the
liver. Cell injury in such cases is usually limited to the region of portal
tracts, which contains vessels that carry blood to the liver from the
digestive tract. In some cases, however, more extensive liver damage can
occur over long periods of time and progress to chronic active hepatitis.
Chronic Active Hepatitis
If damage to the liver is extensive and
cell injury occurs beyond the portal tract, chronic active hepatitis can
develop. Significant liver damage has usually occurred by this time. Liver
cells are destroyed between the portal tract and the central veins in the
liver, and progressive cell damage can build a layer of scar tissue over the
liver, resulting in the condition known as cirrhosis. In such cases, the
entire liver is threatened with malfunction and failure.
What Causes Hepatitis?
Viral Causes of Hepatitis
Most cases of hepatitis are caused by
viruses that attack the liver; most are named with the letters A through G.
It should be noted that the cause of hepatitis is sometimes unexplained,
indicating that additional viruses have not yet been discovered.
Hepatitis A, formerly called infectious
hepatitis, is always acute and never becomes chronic. The virus is excreted
in feces and transmitted in contaminated food and water. Eating shellfish
taken from sewage-contaminated water is a common means of contracting
hepatitis A. It can also be acquired by close contact with individuals
infected with the virus. The hepatitis A virus does not directly kill liver
cells, and experts do not yet know how the virus actually injures the liver.
Hepatitis B and D
The virus for hepatitis B, formerly called
serum hepatitis, is found in semen, blood, and saliva. It is usually spread
by blood transfusions, contaminated needles, and sexual contact. Blood
screening as reduced the risk from transfusions. The virus does not kill
cells directly, but seems to activate cells in the immune system, which
cause inflammation and damage in the liver. Hepatitis D virus can replicate
only by attaching to hepatitis B and therefore cannot exist without the B
virus being present. Between 1% and 10% of hepatitis B patients go on to
develop chronic hepatitis and hepatitis B can become chronic without an
Hepatitis C was the major cause of all
cases of hepatitis resulting from transfusions and most resulting from
intravenous drug use. Because of blood screening, the risk from transfusions
is now 1 in 10,000. It can also be transmitted through injuries in the skin.
It may also be transmitted sexually. About 10% to 60% of acute hepatitis C
patients develop the chronic form, which can also occur without a preceding
Hepatitis E is similar to hepatitis A and
is transmitted by contact with contaminated food or water. It was thought to
be rare, but experts now estimate that up to 20% of people in the US may be
infected, even those who haven't traveled.
Hepatitis G accounts for about 9% of cases
that cannot be diagnosed as hepatitis A through E. It also occurs in about
25% of patients with of hepatitis A, 32% of those with hepatitis B, and 20%
of patients with hepatitis C. Hepatitis G appears always to be chronic, but
to date indications are that it is mild and does not even increase the
severity of any accompanying hepatitis virus.
Other Viruses Causing Hepatitis or Liver Damage
Hepatitis GB has been discovered as a new
distinct form, but it is not known yet whether it causes a serious
condition. A number of other common viruses, including herpes simplex, can
sometimes injure the liver, although they rarely cause severe hepatitis.
Cytomegaloviruses are harmless in most people but can injure the livers in
infants and people with impaired immune systems, such as those with AIDS.