Animation 49.1: The Digestion and Absorption of Fats

INTRODUCTION

Digestion involves the breakdown of complex food molecules into smaller components that can be absorbed and utilized by cells. Digestion begins as soon as food is chewed, when the enzyme amylase begins to break down starches. As food reaches the stomach, the strong acidic (pH 1-3) environment and the enzyme pepsin begin the process of protein digestion. The low pH also helps dissolve the intercellular structures that bind the ingested tissues together.

The digestion of fats begins in the small intestine, where specialized enzymes from the pancreas, and bile salts from the liver play critical roles in fat digestion.

Video titled: Animation 49.1: The Digestion and Absorption of Fats

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CONCLUSION

The digestion of fats begins in the first section of the small intestine, the duodenum. Globules of fat in the acidic chyme coming from the stomach are broken up by intestinal movements, and the smaller droplets become coated with bile molecules that are delivered to the duodenum through the common bile duct. The bile molecules emulsify the fat—they keep the small droplets from aggregating back into large globules. The small fat droplets called micelles offer a large surface area for the action of the fat digesting enzymes, or lipases, that are produced in the pancreas and delivered into the duodenum by the pancreatic duct. The pancreas also delivers a bicarbonate solution into the duodenum to neutralize the acidic chyme. Lipases and other digestive enzymes that work in the intestine require a neutral pH for maximum activity.

The action of pancreatic lipases breaks the triglycerides in the micelles down to free fatty acids, glycerol, and some monoglycerides. These products are fat soluble and easily pass into the epithelial cells lining the intestine. In the endoplasmic reticulum of the intestinal epithelial cells the free fatty acids and monoglycerides are reesterified into triglycerides. These newly formed triglycerides are packaged with cholesterol and coated with proteins to form chylomicrons. The chylomicrons are exported out of the basal ends of the epithelial cells where they are picked up by the tiny terminal vessels of the lymphatic system. The chylomicrons are passed through the lymphatic vessels and delivered into the blood circulation through junctions between the lymphatic system and the circulatory system at the base of the neck.

Textbook Reference: Key Concept 49.3 The Vertebrate Gastrointestinal System Is a Disassembly Line

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