Abstract

The processing of dietary lipids can be distinguished in several sequential steps, including their emulsification, hydrolysis and micellization, before they are absorbed by the enterocytes. Emulsification of lipids starts in the stomach and is mediated by physical forces and favoured by the partial lipolysis of the dietary lipids due to the activity of gastric lipase. The process of lipid digestion continues in the duodenum where pancreatic triacylglycerol lipase (PTL) releases 50 to 70% of dietary fatty acids. Bile salts at low concentrations stimulate PTL activity, but higher concentrations inhibit PTL activity. Pancreatic triacylglycerol lipase activity is regulated by colipase, that interacts with bile salts and PTL and can release bile salt mediated PTL inhibition. Without colipase, PTL is unable to hydrolyse fatty acids from dietary triacylglycerols, resulting in fat malabsorption with severe consequences on bioavailability of dietary lipids and fat-soluble vitamins. Furthermore, carboxyl ester lipase, a pancreatic enzyme that is bile salt-stimulated and displays wide substrate reactivities, is involved in lipid digestion. The products of lipolysis are removed from the water-oil interface by incorporation into mixed micelles that are formed spontaneously by the interaction of bile salts. Monoacylglycerols and phospholipids enhance the ability of bile salts to form mixed micelles. Formation of mixed micelles is necessary to move the non-polar lipids across the unstirred water layer adjacent to the mucosal cells, thereby facilitating absorption.

Highlights

  • Principles of Physiology of Lipid DigestionEmulsification of lipids starts in the stomach and is mediated by physical forces and favoured by the partial lipolysis of the dietary lipids due to the activity of gastric lipase

  • During the last years, studies on lipid digestion and metabolism in farm animals, pigs, have mainly focussed on the provision of dietary energy, since fat is an excellent energy source, which energy value is approximately 2.25 times higher than that of carbohydrates (Maynard et al, 1979)

  • Pancreatic triacylglycerol lipase activity is regulated by colipase, that interacts with bile salts and pancreatic triacylglycerol lipase (PTL) and can release bile salt mediated PTL inhibition

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Summary

Principles of Physiology of Lipid Digestion

Emulsification of lipids starts in the stomach and is mediated by physical forces and favoured by the partial lipolysis of the dietary lipids due to the activity of gastric lipase. The process of lipid digestion continues in the duodenum where pancreatic triacylglycerol lipase (PTL) releases 50 to 70% of dietary fatty acids. Pancreatic triacylglycerol lipase activity is regulated by colipase, that interacts with bile salts and PTL and can release bile salt mediated PTL inhibition. Carboxyl ester lipase, a pancreatic enzyme that is bile salt-stimulated and displays wide substrate reactivities, is involved in lipid digestion. The products of lipolysis are removed from the water-oil interface by incorporation into mixed micelles that are formed spontaneously by the interaction of bile salts. Key Words : Gastric Lipase, Pancreatic Triacylglycerol Lipase, Emulsification, Bile Salts, Colipase, Carboxyl Ester Lipase

INTRODUCTION
ENZYMATIC STEPS
PHYSIOLOGY OF LIPID DIGESTION
THE STOMACH
Contribution of gastric lipolysis to lipid digestion
LIPID DIGESTION IN THE DUODENUM
Role of bile salts
Hydrophilic side
RESTORING EFFECT OF COLIPASE ON BILE
Production of lipoproteins
CARBOXYL ESTER LIPASE
Role of CEL in dietary fat and cholesterol digestion and absorption
Bile salts
Findings
SUMMARY
Full Text
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