Maintenance of the Body
to expel bile into the
. From there bile ﬂows into the
bile duct. Te gallbladder, like most of the liver, is covered by
Bile is the major vehicle for excreting cholesterol from the body,
and bile salts keep the cholesterol dissolved within bile. ±oo much
cholesterol or too few bile salts allows the cholesterol to crystal-
which obstruct the ﬂow of bile from the gallbladder. When the
gallbladder or its duct contracts, the sharp crystals cause agoniz-
ing pain that radiates to the right thoracic region.
Gallstones are easy to diagnose because they show up well
with ultrasound imaging. ±reatments for gallstones include
dissolving the crystals with drugs, pulverizing them with ul-
trasound vibrations (lithotripsy), vaporizing them with lasers,
and the classical treatment, surgically removing the gallbladder.
When the gallbladder is removed, the bile duct enlarges to as-
sume the bile-storing role.
Bile duct blockage prevents both bile salts and bile pigments
from entering the intestine. As a result, yellow bile pigments
accumulate in blood and eventually are deposited in the skin,
causing it to become yellow, or
. Jaundice caused by
blocked ducts is called
, but jaundice may
also reﬂect liver disease (in which the liver is unable to carry out
its normal metabolic duties).
Check Your Understanding
What is a portal triad?
What is the importance of the enterohepatic circulation?
What is the role of the stellate macrophages of the liver?
For answers, see Appendix H.
State the role of pancreatic juice in digestion.
ﬂesh, meat) is
a so², tadpole-shaped gland that extends across the abdomen
(abutting the spleen) to its
, which is encircled
by the C-shaped duodenum (see Figures 23.1 and 23.21). Most
of the pancreas is retroperitoneal and lies deep to the greater
curvature of the stomach.
An accessory digestive organ, the pancreas is important to
the digestive process because it produces enzymes that break
down all categories of foodstuﬀs. Tis exocrine product, called
, drains from the pancreas into the duodendum
via the centrally located
main pancreatic duct
. Te pancreatic
duct generally fuses with the bile duct just as it enters the duo-
denum (at the hepatopancreatic ampulla). A smaller
empties directly into the duodenum just proxi-
mal to the main duct.
Within the pancreas are the
ĭ-ni; singular: acinus), clus-
ters of secretory acinar cells surrounding ducts
Tese cells are full of rough endoplasmic reticulum and exhibit
lin), gives feces a brown color. In
the absence of bile, feces are gray-white and have fatty streaks be-
cause essentially no fats are digested or absorbed.
Te gallbladder is a thin-walled green muscular sac about 10 cm
(4 inches) long. Te size of a kiwi fruit, it snuggles in a shallow
fossa on the inferior surface of the liver (see Figures 23.1 and
23.24) from which its rounded fundus protrudes.
Te gallbladder stores bile that is not immediately needed
for digestion and concentrates it by absorbing some of its water
and ions. When empty, its mucosa is thrown into honeycomb-
like folds (see Figure 23.21) that, like the rugae of the stomach,
allow the organ to expand as it ﬁlls. Its muscular wall contracts
Structure of the enzyme-producing tissue of
Schematic view of one acinus (a secretory unit).
The acinar cells contain abundant zymogen (enzyme-containing)
granules and dark-staining rough ER (typical of gland cells producing
large amounts of protein for export).
pancreatic acinar tissue (155