When we last left our food—now referred to as chyme—it was just leaving the stomach and entering the first part of the small intestine, the duodenum. As food moves from the stomach to the small intestine, the accessory organs of digestion come heavily into play. These include the pancreas, the gallbladder and the liver. In this issue, we’ll discuss only the pancreas.

The pancreas operates within two systems of the body: the endocrine via its secretion of insulin and glucagon, and the digestive through its secretion of digestive enzymes and bicarbonate. This makes it both an endocrine and an exocrine gland, meaning it releases both hormones into the blood and secretions through ducts to act on other organs and tissues.

Anatomically, the pancreas lies deep in the abdomen behind the stomach. Its head is nestled in the curve of the duodenum (the first part of the small intestine) on the right and its tail abuts the spleen on the left. The main pancreatic duct usually joins the bile duct as it enters the small intestine; in a small percentage of people, the two ducts open separately.

While primarily only protein-digesting enzymes are released in the stomach and we’ve had a small amount of both carbohydrate and fat digestion occur to this point, the pancreas is responsible for producing enzymes that digest all three major food types: proteins, fats and carbohydrates.

It accomplishes this through the production of trypsin and chymotrypsin to digest proteins. An enzyme called carboxypolypeptidase digests the smaller fragments of proteins, which are known as peptides. In addition, pancreatic lipase and pancreatic amylase digest fats and starches, respectively. Other enzymes break down various components of fats, such as phospholipase, which splits fatty acids from phospholipids, and cholesterol esterase, which breaks down cholesterol esters.

However, in order to avoid digesting itself, the pancreas doesn’t release fully functioning proteolytic enzymes. Instead, it releases inactive precursors to these enzymes that are not activated until they reach the small intestine. This alteration occurs through activation by additional enzymes.

This ensures that the pancreas is safe from harm and that the enzymes go to work on food, as intended. A safeguard, in the form of a substance called trypsin inhibitor, is produced by the pancreas and further prevents the activation of these enzyme precursors until they reach the duodenum.

In addition to digestive enzymes, the pancreas also secretes an alkaline substance made up of bicarbonate and water. This secretion helps to neutralize the acid manufactured in the stomach. By neutralizing the chyme mixture, this alkaline secretion also inactivates any of the proteolytic enzymes that were secreted in the stomach, since enzymes are active within their own specified range of temperature and pH.

By raising the pH in the small intestine, this also allows the pancreatic enzymes to become active, since they are optimally active at a much higher pH than the enzymes secreted in the stomach.

Since not much carbohydrate or fat digestion has been done up until this point, these enzymes can now go to work on those food particles, preparing them for absorption, packaging and shipping off to the parts of the body that need them for fuel and building materials.