Encyclopedia of Health and Medicine

hereditary nonpolyposis colorectal cancer (HNPCC) 57
• infants born to infected mothers
• people who received organ transplants before
1992 or blood transfusions before 1987 (before
stringent screening practices became available)
• people who work in health care and public
safety
The most effective measures for protecting
against infectious hepatitis are diligent PERSONAL
HYGIENE (especially HAND WASHING) and vaccination.
Vaccines are available to prevent infection with
hepatitis A and hepatitis B. The hepatitis B VACCINE
also protects against hepatitis D, which requires
the hepatitis B virus to replicate. Hepatitis A and
hepatitis E infection confer lifelong immunity.
Measures to reduce the risk for noninfectious hepatitis
center on eliminating or limiting exposure to
hepatotoxic substances including alcohol. The
herb MILK THISTLE (silymarin) helps to protect the
liver from damage and to recover from damage
that occurs. Many health experts recommend that
people who have hepatitis or have exposure to
hepatotoxins take milk thistle.
See also FOOD SAFETY; HEPATITIS PREVENTION; LIVER
CANCER; LIVER DISEASE OF ALCOHOLISM; SHORT BOWEL
SYNDROME.
hepatomegaly An enlarged LIVER. Hepatomegaly
is a symptom of numerous conditions involving
the liver. Its presence or absence has no correlation
to the seriousness of the underlying liver disease.
Because hepatomegaly is a symptom rather
than a condition, it often resolves when the
underlying condition comes under control.
Chronic liver conditions may result in long-term
hepatomegaly.
CONDITIONS THAT CAN RESULT IN HEPATOMEGALY
AMYLOIDOSIS
CIRRHOSIS
HEMATOCHROMATOSIS
INFECTION
LEUKEMIA
LIVER DISEASE OF ALCOHOLISM
REYE’S SYNDROME
sclerosing cholangitis
ANEMIA
congestive HEART FAILURE
HEPATITIS
infectious mononucleosis
LIVER CANCER
LIVER FAILURE
SARCOIDOSIS
STEATOHEPATITIS
See also: HEPATOTOXINS; JAUNDICE; MONONUCLEOSIS,
INFECTIOUS; PORTAL HYPERTENSION; SPLENOMEGALY.
hepatotoxins Substances that damage the LIVER.
A key role of the liver is to metabolize chemicals
that it filters from the BLOOD. In the case of medications,
this releases the therapeutic components
into the bloodstream and channels the waste
byproducts for appropriate elimination. Often the
chemical interactions of these metabolic processes
generate substances that poison the cells of the
liver. Most drugs affect liver function to some
degree; hundreds of them have short-term toxic
effects and dozens cause permanent liver damage.
The most common are ALCOHOL, acetaminophen,
and NONSTEROIDAL ANTI-INFLAMMATORY DRUGS
(NSAIDS). Recreational drugs such as hallucinogenic
mushrooms are especially hazardous to the
liver. Industrial chemicals such as carbon tetrachloride
and numerous environmental pollutants
also cause the death of liver cells (hepatonecrosis).
Elevated levels of key liver enzymes in the
blood provide early indication of hepatotoxicity.
These include aspartate aminotransferase (AST),
alanine aminotransferase (ALT), and glutamate
oxaloacetate transaminase (GOT). Hepatotoxicity
may also result in symptoms similar to those of
HEPATITIS, such as JAUNDICE, NAUSEA, vomiting, and
occasionally FEVER. Damage can be fairly immediate
(within days to weeks of ingestion) or manifest
months later. Regular alcohol consumption
reduces the capacity of the liver to handle toxins,
lowering the threshold at which damage occurs.
Liver function often returns to normal when
ingestion of the toxic substance ends and the liver
completes all metabolic functions related to it,
though hepatotoxic consequences can cause irreversible
loss of liver function and even LIVER FAIL-
URE. Many substances that damage the liver also
damage the KIDNEYS. The herb MILK THISTLE, which
contains silymarin, helps protect the liver from
toxins.
See also ANALGESIC MEDICATIONS; CIRRHOSIS; HAL-
LUCINOGENS; LIVER DISEASE OF ALCOHOLISM; OVERDOSE;
POISON PREVENTION; RENAL FAILURE.
hereditary nonpolyposis colorectal cancer
(HNPCC) A form of COLORECTAL CANCER predisposed
by a mutation in the mlh1 and msh1 genes.
These genes direct DNA repair mechanisms, the
processes cells follow to correct mistakes that
occur when they replicate their DNA codes during