The pancreas contains two distinctive types of glandular tissue, an exocrine component and an endocrine component, which allow the organ to perform two different functions. Exocrine glands secrete their products into a duct system. The ducts, in turn, transport these secretions to a specific target. Acini are the functional units of the exocrine pancreas. Endocrine glands secrete their products directly into the blood, rather than into a duct system. Islets of Langerhans are the functional units of the endocrine pancreas.
NORMAL ANATOMY AND HISTOLOGY OF THE PANCREAS
The pancreas is a retroperitoneal organ located in the upper abdomen and surrounded by a number of important organs and blood vessels. Although the pancreas is one continuous organ, it is thought of as having three anatomic regions based on its spatial relationship to surrounding structures. There are also minor functional differences between the anatomic regions, and certain diseases have a predilection for one region versus another.
The head of the pancreas is nestled within the curvature of the duodenum that abuts the right lateral and right inferior borders of the pancreas. The right borders of the superior mesenteric vessels, which lie directly posterior to the pancreas, mark the transition to the body of the pancreas. The body of the pancreas encompasses the majority of the pancreas and transitions distally into a tapered tail of the pancreas. In addition to the superior mesenteric vessels, the aorta and inferior vena cava lie posterior to the pancreas. Other organs that lie in close proximity to the pancreas include the stomach (anterior to the pancreas), spleen (at the distal tip of the pancreas), and left kidney (posterior to the tail of the pancreas) (Figure 11-1).
Anatomy of the pancreas. Source: McKinley M. and O'Loughlin. Human Anatomy, 2nd ed. New York: McGraw Hill 2007. Figure 20.14.
Before discussing the anatomy of the pancreatic ductal system, it is helpful to first develop a working knowledge of the microscopic anatomy of the pancreas. Low-power examination of the pancreas reveals an organ composed of lobules of tissue (Figure 11-2).
Pancreatic lobule. Grossly and microscopically normal pancreatic tissue has a lobular architecture. The majority of the lobule is composed of acinar tissue. Islets of Langerhans (arrowhead) and a pancreatic duct branch (arrow) are also present.
Exocrine tissue makes up the vast majority of the lobule. The functional unit of the exocrine pancreas is the acinus (pl. acini). Acini are organized collections of secretory cells that surround a central lumen. Acinar cells have peripherally located nuclei and abundant granular cytoplasm and secrete a variety of active enzymes ...