677
CHAPTER SEVENTEEN
Digestive System
dles, from pregnant woman to fetus, or through
blood transfusions or use of blood products. As
many as 60% of individuals infected with the
hepatitis C virus suF
er chronic symptoms.
Hepatitis D
occurs in people already infected
with the hepatitis B virus. It is blood-borne and
associated with blood transfusions and intrave-
nous drug use. About 20% of individuals infected
with this virus die from the infection.
Hepatitis E
virus is usually transmitted in
water contaminated with feces. It most often
aF
ects visitors to developing nations.
Hepatitis G
is rare but seems to account for a
signi±
cant percentage of cases of fulminant hep-
atitis. In people with healthy immune systems, it
produces symptoms so mild that they may not
even be noticed.
A virus usually causes hepatitis, so antibiotic
drugs, eF
ective against bacteria, are not helpful.
Usually, the person must just wait out the symp-
toms. Hepatitis C, however, sometimes responds
to a form of interferon, an immune system bio-
chemical given as a drug.
300 million people worldwide are hepatitis car-
riers. They do not have symptoms but can infect
others. ²ive percent of carriers eventually develop
liver cancer.
Only rarely does hepatitis result from alco-
holism, autoimmunity, or the use of certain drugs.
Usually, one of several types of viruses causes
hepatitis. Viral types are distinguished by the
route of infection, surface features, and whether
the viral genetic material is DNA or RNA. Hepatitis
B virus has DNA; the others have RNA. The viral
types are classi±
ed as follows:
Hepatitis A
spreads by contact with food
or objects contaminated with virus-containing
feces, including diapers. The course of hepatitis A
is short and mild.
Hepatitis B
spreads by contact with virus-
containing body ³
uids, such as blood, saliva, or
semen. It may be transmitted by blood transfu-
sions, hypodermic needles, or sexual activity.
Hepatitis C
accounts for about half of all
known cases of hepatitis. This virus is primarily
transmitted in blood—by sharing razors or nee-
H
epatitis
is an in³
ammation of the liver. It
has several causes, but the various types
have similar symptoms.
²or the ±
rst few days, hepatitis may resem-
ble the ³
u, producing mild headache, low fever,
fatigue, lack of appetite, nausea and vomiting,
and sometimes stiF
joints. By the end of the ±
rst
week, more distinctive symptoms arise: a rash,
pain in the upper right quadrant of the abdomen,
dark and foamy urine, and pale feces. The skin
and sclera of the eyes begin to turn yellow due
to accumulating bile pigments (jaundice). Great
fatigue may continue for two or three weeks, and
then gradually the person begins to feel better.
This is hepatitis in its most common, least
dangerous acute guise. About half a million peo-
ple develop hepatitis in the United States each
year, and 6,000 die. In a rare form called
fulminant
hepatitis,
symptoms are sudden and severe, along
with altered behavior and personality. Medical
attention is necessary to prevent kidney or liver
failure or coma. Hepatitis that persists for more
than six months is termed chronic. As many as
17.3
CLINICAL APPLICATION
Hepatitis
The
bile duct
is formed by the union of the common
hepatic and cystic ducts. It leads to the duodenum, where
the hepatopancreatic sphincter muscle guards its exit (see
F
g. 17.23). This sphincter normally remains contracted, so
as bile collects in the common bile duct it backs up into the
cystic duct. When this happens, the bile fl ows into the gall-
bladder, where it is stored.
Bile salts, bile pigments, and cholesterol become increas-
ingly concentrated as the gallbladder lining reabsorbs water
and electrolytes. The cholesterol normally remains in solu-
tion, but under certain conditions it may precipitate and form
TABLE
17.7
|
Major Functions of the Liver
General Function
Speci±
c Function
General Function
Speci±
c Function
Carbohydrate
metabolism
Polymerizes glucose to glycogen; breaks down
glycogen to glucose; converts noncarbohydrates to
glucose
Protein metabolism
Deaminates amino acids; forms urea; synthesizes plasma
proteins; converts certain amino acids to other amino
acids
Lipid metabolism
Oxidizes fatty acids; synthesizes lipoproteins,
phospholipids, and cholesterol; converts portions of
carbohydrate and protein molecules into fats
Storage
Stores glycogen, vitamins A, D, and B
12
, iron, and blood
Blood ±
ltering
Removes damaged red blood cells and foreign substances
by phagocytosis
Detoxi±
cation
Removes toxins from the blood
Secretion
Secretes bile
Gallbladder
The
gallbladder
is a pear-shaped sac in a depression on the
inferior surface of the liver. It is connected to the
cystic duct,
which, in turn, joins the common hepatic duct (see F
g. 17.23
and reference plate 19). The gallbladder has a capacity of
30–50 milliliters, is lined with columnar epithelial cells, and
has a strong muscular layer in its wall. It stores bile between
meals, concentrates bile by reabsorbing water, and contracts
to release bile into the duodenum when stimulated by chole-
cystokinin from the small intestine.
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