The Pancreas

Pancreas

The pancreasA gland that produces digestive enzymes and hormones like insulin and glucagon. is kind of tucked away between the stomach and the small intestine.  This picture does not do it justice. The pancreas is a retroperitoneal Referring to organs located behind the peritoneum, such as the kidneys and pancreas. organ. It is not in the peritoneal cavity with the other digestive organs. 

We have previously covered the endocrine function of the pancreas. Insulin and glucagonIncreases blood sugar by promoting glycogen breakdown. were secreted directly into blood circulation. The exocrineGlands that secrete substances via ducts (e.g., sweat glands). function of the pancreas involves secreting enzymesProteins that speed up chemical reactions in the body. into the small intestine.  I feel obligated to remind you that what is in the small intestine is not yet in your body.  This is why secretionThe process of moving substances from the blood into the nephron tubule to be excreted in urine. of digestive juices is called an exocrine function. 

Pancreas Macroanatomy

The pancreas is divided into the tail, body, and headRounded proximal end that fits into the acetabulum of the hip bone.. The head is slightly curved and inserted into a loop of the duodenumThe first section of the small intestine where most digestion occurs; it receives chyme, bile, and p. The duodenum is also technically a retroperitoneal organ.  There is a main duct running through the middle of the pancreas.  This duct collects the digestive juices, not insulin and glucagon, and spews them into the small intestine.  Insulin and glucagon are secreted directly into the venule side of capillary beds in the pancreas. 

The pancreatic duct joins with the bileA digestive fluid produced by the liver and stored in the gallbladder; it helps emulsify fats for di duct. Together, they form the common bile duct. This duct then connects everything to the small intestine.  This common bile duct connects to the hepatopancreatic ampulla, or the opening to the duodenum.  The flow of juices from the pancreas and bile from the liverA large organ that produces bile, detoxifies blood, and stores nutrients. is controlled by the hepatopancreatic sphincter. This sphincter is a smooth muscle valve. 

I just want to point out something in this picture that not everyone has.  This little duct here is called the accessory pancreatic duct.  It is an anatomical feature that not everyone has. 

Pancreas Microanatomy

The pancreatic islets, which secrete insulin and glucagon, are separate from the acinar cellsThe basic structural and functional units of life..   Histologically, the acinar cells are clustered around ducts. These are structures called acini (plural) or acinus for the singular form of the word.   The acinar cells secrete digestive enzymes into these blind pockets that are technically glands. All of these glands are connected to the main pancreatic duct. This duct fills with all the digestive enzymes made by the pancreas.  These enzymes are then delivered to the duodenum of the small intestine. They perform chemical digestion on the chymeA semi-fluid mixture of partially digested food and digestive juices that moves from the stomach int received from the stomach.

Pancreatic Juices

Upon entering the duodenum, the chyme is immediately buffered by the pancreatic juices. The small intestine does not have the cellular protection that the stomach has in terms of acidity.  The chyme from the stomach is very acidicA solution with a pH below 7, having a higher concentration of H⁺ ions.. For this reason, the pancreas contains enough bicarbonate(HCO₃⁻) – A crucial buffer in blood that helps maintain pH balance; formed when carbon dioxide. It raises the pHA measure of hydrogen ion concentration in a solution. of the chyme.  This action protects the lining of the small intestine. It also provides the ideal pH for the enzymes contained in pancreatic juices.

The pancreas’s enzymes are released into the small intestine along with the bicarbonate and bile from the gall bladderA muscular organ that stores urine before excretion..  Remember that what’s in the GI tract is not really in your body.  This is why the production of enzymes from the pancreas is called the exocrine function.  So, what’s actually in pancreatic juices?  Well, mostly waterThe universal solvent essential for life.. The chyme becomes even more watered down as the pancreatic juice is added.

The pancreas also contains a ton of enzymes that can finish off the chemical digestion of carbohydrates, lipidsOrganic molecules including fats, oils, and steroids., and proteinsLarge molecules made of amino acids with various functions in the body..  All of these enzymes are able to function at a relatively acidic pH.  You might say: I thought amylase was in saliva?  Yes. It was.  In factA statement based on direct observation that is repeatedly confirmed., saliva and pancreatic juices contain many enzymes with the same names.  However, the amylase in the saliva works at a different pH. The lipase in saliva also operates at a different pH than those in the pancreatic juices. Enzymes called proteases complete the chemical digestion of proteins. They act on proteins left over from the denaturing and the action of pepsin in the stomach. 

So, what the heck is my picture here?  Enzymes.  These are all enzymes and their substrates.  Remember that one enzyme works with one substrate. This was a reflection of the shape of the enzyme’s active siteThe specific region of an enzyme where a substrate binds and a reaction occurs. and the shape of the substrate.