676
UNIT FIVE
17.1
FROM SCIENCE TO TECHNOLOGY
Replacing the Liver
L
ife without a liver is not possible. A person
can survive only a few days once the liver
stops functioning. In fulminant hepatic
failure, for example, an otherwise healthy, young
person suddenly experiences liver failure, caused
by exposure to a toxin, reaction to a drug, or a
viral infection. Jaundice and fatigue progress rap-
idly to coma and death. Once cancer spreads to
the liver, survival is generally only weeks or a few
months.
Livers are in great demand for transplant, but
as is the case for other organs, are scarce. Each
year in the United States, only about 4,500 of the
12,000 or so individuals requiring livers survive
long enough to undergo a transplant. Sometimes
a person can receive part of a liver donated by a
living relative or other close match. The donor
continues to live because only 15% of the liver
need be functional for survival.
A promising solution to the problem of liver
failure in light of the organ shortage is an “extra-
corporeal liver assist device” (ELAD), which can
take over the liver’s blood-cleansing function
until a cadaver organ becomes available, or it can
enable remaining functional liver tissue to suF
-
ciently stimulate regeneration to restore health.
ELAD is a “bioartificial” liver because it has
synthetic as well as biological components. The
device consists of four cartridges ±
lled with hol-
low fibers that house millions of continuously
dividing (“immortalized”) human liver cells (hepa-
tocytes). A patient’s plasma is separated from the
blood and passed through the device, where the
liver cells remove toxins and add liver-secreted
products, such as clotting factors. The plasma is
then ±
ltered, the formed elements of the blood
added back, and the blood reinfused into the
patient. ELAD is essentially a hepatic version of
kidney dialysis.
Bile duct
Bile ductule
Bile canaliculi
Kupffer cell
Hepatic cells
Branch
of hepatic
portal vein
Branch
of hepatic
artery
Blood flow
into liver
Hepatic
sinusoids
Central vein
(blood flow
out of liver)
FIGURE 17.28
The paths of blood
and bile in a hepatic lobule.
Hepatic cells use cholesterol to produce bile salts, and in
secreting these salts, they release some cholesterol into the
bile. Cholesterol by itself has no special function in bile or in
the alimentary canal.
Bile pigments (bilirubin and biliverdin) are breakdown
products of hemoglobin from red blood cells (see chapter 14,
p. 530). These pigments are normally excreted in the bile.
The yellowish skin, sclerae, and mucous membranes of jaun-
dice result from excess deposition of bile pigments.
Jaundice can have several causes. In
obstructive jaundice,
bile ducts
are blocked (as with gallstones or tumors). In hepatocellular jaundice,
the liver is diseased (as in cirrhosis or hepatitis). In
hemolytic jaundice,
red blood cells are destroyed too rapidly (as with a blood transfu-
sion from an incompatible blood group or a blood infection such as
malaria).
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