الفهرس 
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Abstract
INTRODUCTION
Langerhans, while still a medical student in 1869,
first desribed the cells of the pancreatic islets that bear
his name. However, it was not until the isolation of insulin
in 1922 did one of several functions of islet tissue become
apparent. These islets, now known to produce several
different hormones, are estimated to number over one million
in the human pancreas but make up a total of only 1 gram of
tissue. The actual number of islets is probably not
increased in patients wl th hyperinsu linaemia or in those
unusual patients with hyperplasia of the islets. (Brooks,
l9S!I)
In 1902, the first adenoma of the pancreas arlBlng from
an island of Langerhans was desribed by Nicholls. Apparently
no particular clinical symptoms were anociated with such
tumours, and as a result, Heiberg stated in his 1914
hand boo\<. on disease of the pancreas that ”the adenomata of
the pancreatic islets are without clinical significance and
therefore not further discussed.’’! (Heiberg, 1914)
Functioning endocrine tumours of the pancreas are rare.
Many more non-functioning tumours of the same histologic
structure are found incidentally if the pancreas is
carefully investigated at autopsy. The incidence of i a let
tumours in unselected autopsy material appears to be between
0.5~ and 1.5~. Most of these are non-functioning, and others
may be too small to produce significant symptoms. (Warren,
1966)
Identification of the cell type in the pancreatic
islets has undergone a resurgence with discovery and
isolation of new hormon!!l polypeptides and with the
development of new morphological techniques for
investigating the cells that produce them. Today we have A,
or alpha, cells producing glucagon; B, or beta, cells
producing insulin; and D, or delta, cells producing
somatostatin. It 1e believed that there are at least five
types of islet cells. Based on immunocytochemistry, at least
12 hormones or peptides have been detected or postulated in
the pancreatic islet cells. The cells responsible for
insulin, glucagon, gastric inhibitory polypeptide,
pancreatic polypeptide, 11nd somatostatin have been firmly
established. (Brooks, 198!1)
Pancreatic islet cells are components of the
gastroentero-pancreatic part of the diffuse neuroendocrine
system. Cells belonging to this system are commonly referred
to as APUD cells because they share the following
cytochemical characteristics: a high amine content (A); the