Encyclopedia of Health and Medicine

liver cancer 69
and does not contract unless a laxative stimulates
it. Laxatives, and particularly suppositories and
enemas, also can irritate the intestinal mucosa
enough to cause chronic INFLAMMATION.
See also BOWEL MOVEMENT; DIARRHEA; FIBER AND
GASTROINTESTINAL HEALTH; NUTRIENTS; NUTRITIONAL
NEEDS; ROUTES OF ADMINISTRATION.
liver The largest internal organ in the body. Its
soft, spongy tissue spreads like a flattened football
between the DIAPHRAGM and the STOMACH, tucked
protectively beneath the lower ribs on the right
side of the abdomen. Weighing about three and a
half pounds, the liver contains 15 percent of the
body’s blood (about a pint). About 60 percent of
this blood is venous and comes from the gastrointestinal
tract and SPLEEN, entering the liver via the
portal VEIN. The venous blood delivers nutrients
that the liver further metabolizes, the products of
which it then sends back into the bloodstream.
The hepatic ARTERY, which branches directly from
the abdominal AORTA, delivers oxygenated blood to
the liver to fuel the functions of its cells. On the
underside of the liver is the GALLBLADDER, which
concentrates and stores the BILE the liver produces.
The liver’s two main lobes, the small left lobe
and the large right lobe, support an intricate network
of lobules, thousands of tiny communities of
hepatocytes (the cells that carry out the liver’s
functions) that filter NUTRIENTS, wastes, BACTERIA,
and toxins from the blood. The microscopic spaces
between the lobules are the sinusoids, into which
the blood from the portal vein drains. Each lobule
is a hexagonal structure two layers of cells deep
and several cells horizontally and vertically in a
platelike configuration. At the vertical junctions of
the lobules are the portal triads, each containing
three microscopic structures: a venule, an arteriole,
and a bile duct. The portal triads collect the
substances the lobules produce and convey them
to the larger vessels that will carry them out to the
structures of the body. The membranous connective
tissue that envelopes the liver also extends
like a web through the liver, providing a supportive
structure for the lobules, sinusoids, and portal
triads.
The lobules are the work stations of the liver.
They metabolize nutrients and toxins, and synthesize
(manufacture) numerous substances including
amino acids, proteins essential for PLASMA production,
lipoproteins, cholesterol, immune factors,
CLOTTING FACTORS, LYMPH, and bile. The lobules convert
GLUCOSE to glycogen, a storage form of glucose
the body can draw from when blood levels of glucose
fall, and glycogen back to glucose, processes
that integrate closely with the balance of glucose
and INSULIN in the blood. The lobules also deconstruct
old erythrocytes (red blood cells) to recycle
the iron and BILIRUBIN they contain. Specialized
phagocytic (“cell eating”) cells, called Kupffer
cells, reside in the sinusoids to consume bacteria
and cellular waste. The liver stores iron, glycogen,
vitamin A and vitamin B 12 , and other chemicals
the body needs for cellular activities. The liver is
unique among the body’s organs in its ability to
regenerate itself. This extraordinary capacity
speaks to the significant extent of damage that
must take place to permanently destroy liver tissue.
Even so, the liver can meet the needs of the
body as long as 25 percent of its cells remain functional.
COMMON CONDITIONS THAT CAN AFFECT THE LIVER
BILIARY ATRESIA
CIRRHOSIS
HEPATIC ABSCESS
HEPATITIS
LIVER DISEASE OF ALCOHOLISM
PORTAL HYPERTENSION
PRIMARY SCLEROSING CHOLANGITIS
CHOLESTASIS
DIABETES
HEPATIC CYST
LIVER CANCER
PANCREATITIS
PRIMARY BILIARY CIRRHOSIS
STEATOHEPATITIS
For further discussion of the liver within the
context of gastrointestinal structure and function,
please see the overview section “The Gastrointestinal
System.”
See also BILE DUCTS; ESOPHAGEAL VARICES;
HEPATOMEGALY; HEPATOTOXINS; JAUNDICE; LIVER FAILURE;
LIVER FUNCTION TESTS; LIVER TRANSPLANTATION; NUTRI-
TIONAL NEEDS; VITAMINS AND HEALTH.
liver cancer Malignant growths in the LIVER.
Liver CANCER may be primary (originates in the
liver) or secondary (metastasizes, or spreads, from
other locations in the body). Primary liver cancer
is less common than metastatic liver cancer. Most
primary liver cancer develops as a complication of
chronic HEPATITIS B or hepatitis C INFECTION, conditions
that repeatedly damage liver tissue, and