Structure and Function of the Endocrine Pancreas

The cellular composition of the pancreas has been described in great detail.10,28,35 The bulk of the gland consists of acinar cells that synthesize and release pancreatic digestive enzymes (thereby providing the exocrine function). Interspersed within the acinar tissues are smaller clumps of tissue known as the islets of 

Langerhans. These islets contain cells that synthesize and secrete pancreatic hormones, thus constituting the endocrine portion of the gland. 

The pancreatic islets consist of four primary cell types alpha (A) cells, which produce glucagon beta (B) cells, which produce insulin delta (D) cells, which produce somatostatin and (F) cells, which produce pancreatic polypeptide. As previously mentioned, this chapter focuses on the functions of insulin and glucagon. The exact physiologic roles of the other pancreatic hormones are not entirely clear. For example, the function of the pancreatic polypeptide released from pancreatic F cells remains to be determined. 

Insulin is a large polypeptide of 51 amino acids arranged in a specific sequence and configuration. The primary effect of insulin is to lower blood glucose levels by facilitating the entry of glucose into peripheral tissues. The effects of insulin on energy metabolism, specific aspects of insulin release, and insulin s mechanism of action are discussed here. 

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