P

pancreas An elongated gland with both
endocrine and exocrine functions that lies beneath
the STOMACH on the upper left side of the
abdomen, beneath the lower ribs. Both realms of
function play roles in digestion, though the
endocrine functions of the pancreas are also sig-
nificant for maintaining the body’s GLUCOSE-INSULIN
balance and for regulating cellular use of glucose.
The main body of the pancreas is a loose collec-
tion of secretory cells, looking somewhat like a
mass of fish eggs, that produce DIGESTIVE ENZYMES
and juices. These cells organize in lobular forma-
tions, called acini, around ducts that channel their
secretions to the main pancreatic duct coursing
through the center of the pancreas (hence their
designation as exocrine). The pancreatic duct joins
the common BILEduct from the GALLBLADDERjust
before the DUODENUM (the first segment of the
SMALL INTESTINE), adding its juices to the bile that
then flows into the duodenum.
Interspersed among the secretory cells are about
a million clusters of specialized cells that produce
the hormonesINSULIN, GLUCAGON, and SOMATOSTATIN.
Called the ISLETS OFLANGERHANS, these clusters are
the endocrine glands of the pancreas. An extensive
BLOODsupply infiltrates the islets, which secrete
their hormones directly into the bloodstream
(hence their designation as endocrine). These hor-
mones regulate numerous functions of METABOLISM
throughout the body, including many that take
place in the gastrointestinal system.

Pancreatic Enzymes and Juices
The pancreas produces numerous enzymes essen-
tial for digestion. DIGESTIVE HORMONEStrigger their
release. Key among the digestive enzymes are

• proteases, notably trypsin and chymotrypsin,
  which break down proteins; to protect itself

from these proteases hydrolyzing its own tissue,

the pancreas secretes them in proenzyme

forms, trypsinogen and chymotrypsinogen, that

an enzyme in the duodenum, enterokinase,

activates

• pancreatic lipase, which breaks down dietary
  triglyceride into fatty acid molecules the intes-
  tinal mucosa can absorb


• amylase, which breaks down dietary starches
  (plant-based stored carbohydrates) into disac-
  charides (multiple molecule sugars) in prepara-
  tion for further digestion later in the small
  intestine


• ribonuclease and deoxyribonuclease, which
  break down nucleic acids (chemicals that facili-
  tate the body’s use of proteins)


• elastase, which facilitates the break down of
  proteins into amino acids


• bicarbonate, which neutralizes gastric acid in the
  chyme (mixture of food and gastric juices) that
  flows from the stomach into the duodenum

Pancreatic Hormones

The primary hormones the pancreas produces are

insulin, glucagon, and somatostatin. Insulin is key

to carbohydrate and lipid (fatty acid) metabolism,

in the gastrointestinal tract as well as at the cellu-

lar level throughout the body. The pancreas

releases insulin in response to digestive hormones

the gastrointestinal tract secretes as food enters

the various stages of digestion. Insulin regulates

glucose levels in the blood by controlling how

much, and when, glucose enters the cells. It also

signals the LIVERto convert excess glucose to the

storage form glycogen. Somatostatin slows the

release of insulin. Glandular tissue in the intes-

tinal mucosa also produces somatostatin, which

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