The digestion of certain fats begins in the mouth, where lingual lipase breaks down short chain lipids into diglycerides. The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas, and bile from the liver, to enable the breakdown of fats into fatty acids.
The complete digestion of one molecule of fat a triglyceride results in three fatty acid molecules and one glycerol molecule. Carbohydrate digestion : A diagram of the action of the oligosaccharide-cleaving enzymes in the small intestine. Lipid digestion : Lipid digestion involves the formation of micelles in the presence of bile salts, and the passage of micelles and fatty acids through the unstirred layer.
The diagram depicts dietary fat at the top, with pancreatic lipase and bile salts forming micelles that will pass through the unstirred layer at the bottom of the diagram. Privacy Policy. Skip to main content. Digestive System.
Search for:. Chemical Digestion. Mechanisms of Chemical Digestion Chemical digestion is the enzyme-mediated, hydrolysis process that breaks down large macronutrients into smaller molecules. Learning Objectives Differentiate among the methods used to chemically break down food molecules.
Key Takeaways Key Points Carbohydrates are mainly taken in the form of amylose and glycogen. Amylases hydrolyze the long carbohydrate chains that break amylose down into disaccharides, and glycogen into polysaccharides. The enzymes in the small intestine then break these down to monosaccharides. Proteins are digested by hydrolysis of the carbon—nitrogen C—N bond. Peptidases are secreted in an inactive form, to prevent auto-digestion. As a result, the fats become tiny droplets and separate from the watery components.
In the stomach, gastric lipase starts to break down triacylglycerols into diglycerides and fatty acids. Within two to four hours after eating a meal, roughly 30 percent of the triacylglycerols are converted to diglycerides and fatty acids.
However, even amid all of this activity, very little fat digestion occurs in the stomach. As stomach contents enter the small intestine, the digestive system sets out to manage a small hurdle, namely, to combine the separated fats with its own watery fluids.
The solution to this hurdle is bile. Bile contains bile salts, lecithin, and substances derived from cholesterol so it acts as an emulsifier.
It attracts and holds on to fat while it is simultaneously attracted to and held on to by water. Emulsification increases the surface area of lipids over a thousand-fold, making them more accessible to the digestive enzymes.
Once the stomach contents have been emulsified, fat-breaking enzymes work on the triacylglycerols and diglycerides to sever fatty acids from their glycerol foundations.
As pancreatic lipase enters the small intestine, it breaks down the fats into free fatty acids and monoglycerides. Yet again, another hurdle presents itself. How will the fats pass through the watery layer of mucous that coats the absorptive lining of the digestive tract? As before, the answer is bile. Bile salts envelop the fatty acids and monoglycerides to form micelles. Micelles have a fatty acid core with a water-soluble exterior. This allows efficient transportation to the intestinal microvillus.
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Hepatic lipase activity is increased in non-alcoholic fatty liver disease beyone insulin resistance. Diabetes Metab Res Rev. Olivecrona G, Olivecrona T. Triglyceride lipases and atherosclerosis. Curr Opin Lipidol. Elevated serum lipase levels in patients with dyspepsia of unknown cause in general practice.
Med Princ Pract. Petridou, A. Acute changes in triacylglycerol lipase activity of human adipose tissue during exercise. J Lipid Res. Roxas M. The role of enzyme supplementation in digestive disorders. Lipase enzymes break down fat into fatty acids and glycerol. Digestion of fat in the small intestine is helped by bile , made in the liver.
Bile breaks the fat into small droplets that are easier for the lipase enzymes to work on. Bile is not an enzyme. Minerals, vitamins and water are already small enough to be absorbed by the body without being broken down, so they are not digested.
Digestive enzymes cannot break down dietary fibre, which is why the body cannot absorb it.
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