386 Chapter 16
Contracting muscles (^) Bolus
(peristaltic wave) (^)
Stomach
(A) Bolus is swept along esophagus by
peristaltic contractions; lower esophageal
sphincter (arrows) is closed
(^) ®
Learning
Cengage ©
Peristaltic wave
reaches end of
esophagus
(B) Lower esophageal sphincter (arrows) opens;
bolus moves into stomach
(^) ®
Learning
Cengage ©
Figure 16- 8 Swallowing. (A) Bolus is pushed through the esophagus by peristaltic waves; lower esophageal sphincter is
closed.
(B) Lower esophageal sphincter is open, and the bolus enters the stomach.
contents into the duodenum (doo-oh-DEE-num) of the
small intestine approximately 2 to 6 hours after inges-tion.
Foods high in carbohydrates pass through the stom-ach first
because their digestion begins in the mouth via the salivary
enzyme amylase. Protein foods pass through somewhat
more slowly because their digestion begins in the stomach.
Foods containing large amounts of fats take the longest to
pass into the duodenum. The stomach participates in the
absorption of some water and salts. Certain drugs, such as
aspirin and alcohol, can also be absorbed in the stomach.
The next step is chemical digestion in the small in-
testine. This process depends on secretions from intes-tinal
glands and on secretions of the two large accessory glands
of the system, the pancreas, and the liver and its
gallbladder.
The Pancreas
The pancreas is a soft, oblong gland about 6 inches long
and 1 inch thick (Figure 16-10). It is found beneath the
great curvature of the stomach and is connected by a
duct to the duodenum of the small intestine. The pan-creas
is divided into a head (the part closest to the duodenum),
the body (the main part), and the tail. -Internally, the
pancreas is made up of clusters of glan-dular epithelial
cells. One group of these clusters, the islets of
Langerhans, or the pancreatic islets, form the en-
docrine portions of the gland and are therefore part of the
endocrine system. Some of these clusters consist of alpha
cells that secrete the hormone glucagon (GLOO-kah-
gon). Other clusters consist of beta cells that -secrete the
hormone insulin (review Chapter 12). The other masses of
cells are called the acini (AS-in-eye), which are the
exocrine glands of the organ. The acini release a mix-ture
of digestive enzymes (lipases, carbohydrases, and
proteases) called the pancreatic juice, which leaves the
pancreas through a large main tube called the pancreatic
duct, or duct of Wirsung. The duct cells secrete sodium
bicarbonate. In most individuals, the pancreatic duct unites
with the common bile duct of the liver and enters the
duodenum in a common duct, originally called the
ampulla (am-PULL-lah) of Vater but now is called the
hepatopancreatic- ampulla.