CHAPTER 16
Digestive Glands and Associated Organs
321
T. Yang
Left hepatic
duct
Common
hepatic duct
Cystic
duct
Right hepatic
duct
Gallbladder
Hepatopancreatic
ampulla (of Vater)
Major
duodenal papilla
Bile
duct
Main pancreatic
duct
Main
pancreatic
duct
Columnar
epithelium
Smooth muscle
Adventitia
Muscularis
Mucosa
A
Figure 16-15A.
Gallbladder.
H&E,
3
34; inset
3
99
The
gallbladder
is a pear-shaped, saclike organ that stores, concentrates, and releases bile. It connects directly to the cystic duct, which is an extension
of the gallbladder. Bile from the right and left hepatic ducts drains into the common hepatic duct, which connects to the cystic duct and enters the gall-
bladder. The gallbladder releases bile in response to
cholecystokinin
. The gallbladder has a thin wall, which is composed of three layers. (1) The
mucosa
is the innermost layer, lined by simple columnar epithelium, with many microvilli on the apical surfaces and a lamina propria (loose connective tissue)
beneath the epithelium. The mucosa has many branching folds. (2) The
muscularis
consists of interlacing longitudinal and obliquely oriented bundles
of smooth muscle F bers. The contraction of these muscle F bers helps empty bile through the cystic duct into the bile duct. The
spiral valve of Heister
(smooth muscle at neck of the gallbladder) controls the opening or closing of the gallbladder. The bile duct joins the pancreatic duct at the hepatopancre-
atic ampulla, and bile enters the duodenum through the major duodenal papilla. (3) The
serosa
is a connective tissue that covers most of the gallbladder.
It contains mesothelium and is continuous with the covering of the liver. The
adventitia
attaches the gallbladder to the liver and lacks a mesothelium.
Gallbladder
Microvilli
Microvilli
Microvilli
Lumen
Lumen
Lumen
Mitochondria
Columnar cells
Nuclei of
Nuclei of
columnar cells
columnar cells
Nuclei of
columnar cells
Basal
Basal
lamina
lamina
Basal
lamina
Interdigitating
lateral membranes
B
Figure 16-15B.
Epithelial cells lining the gallbladder.
EM,
3
5,291; inset
3
2,278
There are many short
microvilli
on the apical surfaces of the columnar cells that line the
gallbladder
. Numerous microvilli indicate the function of
these cells, which is to absorb water from bile in the lumen and transport it into the interstitial tissue. Concentrating bile is one of the main functions
of the gallbladder. The
interdigitating lateral membranes
at the lateral borders of the columnar cells are typical of water-transporting cells. Many
mitochondria
are in the cytoplasm of these cells, and are more numerous in the superior region. The
inset
shows the basal region of the epithelium.
Oval-shaped nuclei are located close to the basal lamina.
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