340
UNIT 3
Organ Systems
Islets of
Islets of
Langerhans
Langerhans
Islets of
Langerhans
Exocrine
Exocrine
secretory cells
secretory cells
Exocrine
secretory cells
Small
Small
artery
artery
Small
artery
Septum
Septum
Septum
Interlobular
Interlobular
duct
duct
Interlobular
duct
Connective
Connective
tissue
tissue
Connective
tissue
A
Islet of
Islet of
Langerhans
Langerhans
Islet of
Langerhans
Exocrine
secretory cells
Endocrine
secretory cells
Exocrine
Exocrine
gland
gland
Exocrine
gland
Exocrine
Exocrine
gland
gland
Exocrine
gland
Capillaries
Capillaries
Capillaries
Islet of
Langerhans
B
Endocrine Pancreas
Figure 17-14A.
Islets of Langerhans, endocrine pancreas.
H&E,
3
39
The pancreas has
endocrine
and
exocrine
components. The
endocrine
component consists of the
islets of Langerhans
, which are clusters of
endocrine cells within a capillary network. There are numerous pale-
staining islets of Langerhans scattered throughout the pancreas, and
each of them is surrounded by an eosinophilic
exocrine
component
of the pancreas as shown here. A connective tissue septum divides
the pancreas into lobules. Two interlobular ducts, surrounded by the
connective tissue, belong to the exocrine pancreas, from which they
carry secretions. The endocrine pancreas does not have ducts; the
hormones (
insulin
and
glucagon
) secreted by the islets of Langerhans
are released into the capillaries and from there into the blood circula-
tion. Insulin and glucagons play important roles in regulating blood
glucose levels. Insulin stimulates glucose entry in many cells, thereby
regulating carbohydrate metabolism and lowering blood glucose lev-
els. Glucagon enhances the synthesis and release of glucose from the
liver into the blood, thus increasing blood glucose levels.
Figure 17-14B.
Islets of Langerhans, endocrine pancreas.
H&E,
3
462
There are four types of endocrine cells in the
islets of Langerhans
:
alpha cells
,
beta cells
,
delta cells
, and
PP cells
. It is difF
cult to
distinguish among them in H&E stain. However, the beta cells are usually distributed throughout the islets; the other three types
of cells are commonly found at the periphery of the islets.
Alpha cells
secrete
glucagon
,
beta cells
secrete
insulin
,
delta cells
secrete
somatostatin
and
gastrin
, and
PP cells
secrete
pancreatic polypeptide
. Secretion of
insulin
occurs in response to high blood glucose
levels; secretion of
glucagon
occurs in response to lower blood glucose levels.
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