Figure 1723

Photomicrographs of islets of Langerhans. a. In this routine H&E preparation, it is difficult to identify specific islet cell types without special stains. At best, one can identify small cells (arrows) at the periphery of the islet that are probably A cells. X360. b. This photo

micrograph shows an islet of Langerhans stained with a special Grimelius silver stain that reacts with glucagon-secreting cells. The silver-impregnated A cells are arranged around the periphery of the islet. x360.

table 17.2. Principal Cell Types in Pancreatic Islets

Cytoplasmic Staining with

Cell Type % Mallory-Azan Product Granules (TEM)

A 15-20 Red Glucagon About 250 nm; dense, eccentric core surrounded by light substance

B 60-70 Brownish orange Insulin About 300 nm; many with dense, crystalline (angular) core surrounded by light substance

D 5-10 Blue Somatostatin About 325 nm; homogeneous matrix table 17.3. Minor Cell Types in Pancreatic Islets

Cell Type

D-1 cell EC cell"

Secretion

Pancreatic polypeptide

Vasoactive intestinal peptide (VIP)

Secretin, motilin, substance P

Location (in Addition to Islet)

Also in exocrine acini and duct epithelium®

Also in exocrine acini and duct epithelium"

Actions

Stimulates gastric chief cells, inhibits bile secretion and intestinal motility, inhibits pancreatic enzymes and HC03" secretion

Similar to those of glucagon (hyperglycemic and glycogenolytic); also affects secretory activity and motility in gut; stimulates pancreatic exocrine secretion

Secretin: acts locally to stimulate HC03_ secretion in pancreatic juice and pancreatic enzyme secretion Motilin: increases gastric and intestinal motility Substance P: has neurotransmitter properties

"PP, protein polypeptide; EC, enterochromaffin cell.

This localization further emphasizes the ontogeny of the pancreas from the embryonic gut.

pancreatic acini

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