Content Reviewers:Rishi Desai, MD, MPH
The pancreas is a large gland that has both exocrine and endocrine functions.
The majority of the pancreas consists of exocrine glands that produce about 1.5 liters of alkaline digestive enzymes daily, which is secreted directly into the duodenum.
The pancreas, also contains small endocrine cells found in clusters called islets of Langerhans, which typically stain lighter than the pancreatic tissue around it.
The pancreas has a thin collagenous capsule that surrounds the entire pancreas, although only portions of it can be seen in this image.
The capsule also extends into the pancreas as septa, forming lobules.
This section of the pancreas was prepared with Azan stain, which stains collagen blue-ish purple color in order to highlight structures such as the capsule, septa, as well as the connective tissue that surrounds large blood vessels.
Azan stain will also stain the connective tissue surrounding interlobular ducts a similar color as well.
But these ducts can be differentiated from the blood vessels by the presence of digestive enzymes instead of red blood cells within their lumen as well as their distinct epithelium that lines the lumen.
The epithelium consists of simple columnar cells in this image, but some ducts may also consist of stratified columnar or stratified cuboidal epithelium instead.
To the right of the interlobular ducts is an adipocyte.
The adipocytes actually increase in number within the pancreas as individuals age, which is a normal finding that’s caused by pancreatic atrophy over time.
The main functional tissue of the pancreas is called the parenchyma.
If we take a closer look at this slide stained with hematoxylin and eosin, or H&E for short, we can see that the majority of the parenchyma consists of the exocrine portion of the pancreas. The exocrine secretory cells are arranged in groups that resemble a berry surrounding a central lumen.
In latin acini means “berries,” which is why the groups of exocrine cells are called acini. we can see that the secretory cells are pyramid-shaped and their nuclei are found slightly closer to their bases.
This particular slide was stained with H&E, which allows us to see the purple, basophilic rough endoplasmic reticulum seen closer to the base of each secretory cell; and the pink eosinophilic secretory granules at the apices are inactivated enzymes called zymogens.
In acute pancreatitis, it’s the exocrine secretory cells that are damaged and end up releasing their enzymes into their immediate surroundings.
These strong digestive enzymes cause additional damage to pancreatic tissue and leads to severe inflammation as well.
The center of the acini will sometimes contain one or more cells with a paler appearance.
These cells are called centroacinar cells and they’re actually extensions of the small ducts that drain the digestive enzymes produced by the acini, called intercalated ducts.
The presence of centroacinar cells is a unique feature of the exocrine pancreas and is also an identifying marker that indicates the beginning of the intercalated ducts.
These ducts are lined by simple cuboidal epithelium and can be seen in this image as a linear arrangement of cuboidal cells.
And in this cross-section of the intercalated duct, you can see the circular duct that is formed by the cuboidal cells.