Cirrhosis
(Cirrhosis of the
Liver)
Medical Author: Dennis Lee, MD
Medical Editor: Jay W. Marks, MD
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The Relationship of Chronic Viral Hepatitis,
Alcoholism, and Cirrhosis to Liver Cancer
Medical Author: Jay W. Marks, M.D.
Medical Editor: Leslie J. Schoenfield, MD, PhD
Cancer can start within the liver (primary liver cancer or
hepatocellular cancer) or spread to the liver (metastatic liver cancer) from
other sites, such as the colon. Cancer that starts in the liver, which I
will refer to simply as liver cancer, is the fifth most common cancer in the
world. In the U.S., it is among the 10 most common cancers. This cancer is more
frequent among Native Americans, Asians, Pacific Islanders, and Hispanics than among
Caucasians.
Liver cancer is a bad cancer. It has frequently spread
beyond the liver by the time it is discovered, and only 5% of patients with
liver cancer that has begun to cause symptoms survive even five years without treatment.
The only hope for patients who are at risk for liver cancer is regular surveillance so
that the cancers can be found early. Early cancers can be treated by
surgical removal (resection), destruction of the individual tumors, or liver transplantation. Although
the current techniques for surveillance are not very good at detecting early
liver cancer, newer techniques are being tested and appear to be better.
The most common diseases associated with liver cancer
are chronic viral hepatitis, alcoholism, and cirrhosis (scarring of
the liver).
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What is cirrhosis?
Cirrhosis is a complication of many liver diseases that
is characterized by abnormal structure and function of the liver. The diseases
that lead to cirrhosis do so because they injure and kill liver cells, and the
inflammation and repair that is associated with the dying liver cells causes
scar tissue to form. The liver cells that do not die multiply in an attempt to
replace the cells that have died. This results in clusters of newly-formed liver
cells (regenerative nodules) within the scar tissue. There are many causes of
cirrhosis; they include chemicals (such as alcohol, fat, and certain
medications), viruses, toxic metals
(such as iron and copper that accumulate in
the liver as a result of genetic diseases), and autoimmune liver disease in
which the body's immune system attacks the liver.
Why does cirrhosis cause problems?
The liver is an important organ in the body. It performs
many critical functions, two of which are producing substances required by the
body, for example, clotting proteins that are necessary in order for blood to clot, and
removing toxic substances that can be harmful to the body, for example, drugs.
The liver also has an important role in regulating the supply to the body of
glucose (sugar) and lipids (fat) that the body uses as fuel. In order to perform
these critical functions, the liver cells must be working normally, and they
must have an intimate relationship with the blood since the substances that are
added or removed by the liver are transported to and from the liver by the
blood.
The relationship of the liver to the blood is unique.
Unlike most organs in the body, only a small amount of blood is supplied to the
liver by arteries. Most of the liver's supply of blood comes from the intestinal
veins as the blood returns to the heart. The main vein that returns blood from the intestines is called the
portal vein. As the portal vein passes through the liver, it breaks up into
increasingly smaller and smaller veins. The tiniest veins (called sinusoids
because of their unique structure) are in close contact with the liver cells. In
fact, the liver cells line up along the length of the sinusoids. This close
relationship between the liver cells and blood from the portal vein allows the
liver cells to remove and add substances to the blood. Once the blood has passed
through the sinusoids, it is collected in increasingly larger and larger veins
that ultimately form a single vein, the hepatic vein that returns the blood to
the heart.
In cirrhosis, the relationship between blood and liver
cells is destroyed. Even though the liver cells that survive or are newly-formed
may be able to produce and remove substances from the blood, they do not have
the normal, intimate relationship with the blood, and this interferes with the
liver cells' ability to add or remove substances from the blood. In addition,
the scarring within the cirrhotic liver obstructs the flow of blood through the
liver and to the liver cells. As a result of the obstruction to the flow of
blood through the liver, blood "backs-up" in the portal vein, and the pressure
in the portal vein increases, a condition called portal hypertension. Because of
the obstruction to flow and high pressures in the portal vein, blood in the
portal vein seeks other veins in which to return to the heart, veins with lower
pressures that bypass
the liver. Unfortunately, the liver is unable to add or remove substances from
blood that bypasses it. It is a combination of reduced numbers of liver cells,
loss of the normal contact between blood passing through the liver and the liver
cells, and blood bypassing the liver that leads to many of the manifestations of
cirrhosis.
A second reason for the problems caused by cirrhosis is the disturbed
relationship between the liver cells and the channels through which bile flows. Bile is a
fluid produced by liver cells that has two important functions: to aid in
digestion and to remove and eliminate toxic substances from the body. The bile
that is produced by liver cells is secreted into very tiny channels that run
between the liver cells that line the sinusoids, called canaliculi. The
canaliculi empty into small ducts which then join together to form larger and
larger ducts. Ultimately, all of the ducts combine into one duct that enters the
small intestine. In
this way, bile gets to the intestine where it can help with the digestion of
food. At the same time, toxic substances contained in the bile
enter the intestine and then are eliminated in the stool. In cirrhosis, the
canaliculi are abnormal and the relationship between liver cells and canaliculi
is destroyed, just like the relationship between the liver cells and blood in
the sinusoids. As a result, the liver is not able to eliminate toxic substances
normally, and they can accumulate in the body. To a minor extent, digestion in
the intestine also is reduced.
Next: What are the signs and symptoms of cirrhosis? »
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