Histology Fact Sheet: Pancreas

The pancreas is both an endocrine and exocrine organ. 

The duct of Wirsung is the pancreatic duct.  The opening of the pancreatic duct into the duodenum is at the ampulla of Vater.

Histology of the Exocrine Pancreas

The exocrine portion of the pancreas secretes digestive enzymes.  These enzymes go through a duct to enter into the duodenum. The acini is the exocrine portion of the pancreas.

Histology of Endocrine Pancreas

The endocrine portion of the pancreas secretes hormones.  On a histology slide, the endocrine portion of the pancreas can be seen as the Islets of Langerhans. Islets of Langerhans occur most frequently in the tail of the pancreas.  Within the islets, there are several cell types. The alpha cells secrete glucagon.
The beta cells secrete insulin. The delta cells secrete somatostain.

Glucagon is released in response to a low concentration of glucose in the blood. Insulin is released in response to a high concentration of glucose in the blood.

Histology slide of the pancreas
Histology slide courtesy of Histology-World!

Sources:

Histology: A Text and Atlas
Michael H. Ross/Edward J. Reith