What is the pathophysiology of exocrine pancreatic insufficiency (EPI)?

Updated: Aug 12, 2021
  • Author: Samer Al-Kaade, MD; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

The GI tract is responsible for digesting and absorbing food. [8] Lipids provide the richest source of energy for the body, with 9 calories in every gram of fat; in comparison, carbohydrate and protein contains 4 calories per gram. Whereas protein and carbohydrate begin to undergo digestion in the stomach, triglycerides remain mostly unchanged until they reach the small intestine. Intragastric breakdown accounts for approximately 10% of total lipid digestion. [8]

The pancreatic enzymes responsible for lipid digestion are inactivated when the pH drops below 5; thus, before digestion can continue in the duodenum, the acidic contents of the stomach must be neutralized. Fortunately, the pancreas also secretes bicarbonate, which increases the pH of the duodenal contents.

The exocrine pancreas produces 3 main types of enzymes: amylase, protease, and lipase. [3] Under normal physiologic conditions, pancreatic enzymes (specifically, lipase) break the undigested triglycerides into fatty acids and monoglycerides. Bile salts then solubilize these breakdown products to form micelles, which are vehicles for absorbing lipid breakdown products. [8] Normal fat digestion also depends on postprandial synchrony between delivery of nutrients to the duodenum and discharge of pancreatic enzymes. [3]

Pancreatic secretion is governed by neural and hormonal mechanisms. The hormones responsible for regulation are secretin and cholecystokinin (CCK). Secretin is secreted in response to acid in the duodenum, causing duct cells to release water and bicarbonate; CCK is secreted in response to protein and fat in the small intestine, stimulating acinar cells to release the pancreatic enzymes (see the image below).

Factors controlling release of pancreatic secretio Factors controlling release of pancreatic secretions. Image courtesy of Wikimedia Commons.

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