Question

Elaborate on the chemical digestion of fats, including specific enzymes.                               

Answer 1

Fats can be classified into simple or neutral fats(triglycerides), compound fats (phospholipids, sphingomyelins, galactolipids ) and associated fats.

Fat of food consists mainly of neutral or simple fats along with small amounts of free fatty acids, lecithin and cholesterol esters.

Chemical digestion of fats:

• Mouth: Usually there is no digestion of fats in the mouth. But activated salivary lipase in the stomach can digest as much as 30% of dietary triglycerides.
• Stomach: In the stomach there is gastric lipase. It is a weak fat splitting enzyme. It acts at a favorable pH of 4 to 4.5 and gets inactivated at a pH of 2.5 ( gastric pH is 1-2). Hence, fat digestion in the stomach in special conditions only (eg, in achlorhydria).
• Small intestine: Major hub for digestion of fats. This is done with the help of pancreatic lipase and bile salts (secreted at the 2nd part of the duodenum).
  • Pancreatic lipase- It is found in the [pancreatic juice that is being secreted in the duodenum. This is alkaline in nature ( ph 7.8 to 8.4). Now this pancreatic juice converts the acidic chyme ( pH 6.0) into slightly alkaline chyme having a pH of around 7.0. Alkaline chyme acts as the best condition for the action of pancreatic lipase. This converts Triglycerides into monoglycerides and fatty acids. And Phospholipase converts phospholipids into fatty acids.
  • Bile sats- Bile salts are quite important in the digestion of fats as they make the fats easy to break down. They have a detergent action on the fats and emulsify them. They do this by lowering the surface tension. Lipase actually cannot act directly on the fat molecules, but it acts at the interface between the fat particles and water ( emulsified fats)
  • Cholesterol esterase: Along with pancreatic lipase, cholesterol esterase from the succus entericus hydrolyses these esters to cholesterol.

In this way the whole process of fat digestion is carried out in the body.