Question 78: How do carbohydrates, proteins and fats get digested in human beings?
Answer:
Digestion of carbohydrates: Digestion of carbohydrates starts in the buccal cavity where the food receives saliva contains salivary amylase enzyme which converts starch and glycogen into maltose, isomaltose and dextrins. This salivary digestion continues in the stomach and then completes in the small intestine where the food meets two juices:- pancreatic juice and Intestinal juice. These juices help in the breakdown of the sugar molecules to glucose and galactose.
Digestion of Proteins: Protein digestion starts in the stomach and completes in the small intestine. Proteins are first digested by pepsin enzymes which are secreted by the gastric glands present in the stomach. Gastric glands secrete gastric juice which contains HCL and mucus; HCL produce appropriate pH for the digestion of proteins. In the small intestine, food receives bile, pancreatic juice and intestinal juice from liver, pancreas and from intestinal glands respectively with the basic hydrogen ion concentration. This alkalinity stops the action of pepsin enzyme. Then pancreatic juice secretes trypsin and chymotrypsinogen enzyme where complete digestion of proteins takes place.
Digestion of fats: Fats and oils are digested by the lipases. This digestion starts in the stomach and completes in the small intestine.
In the stomach, gastric juices contain gastric lipase which converts fats into monoglycerides. In the small intestine, bile juice is secreted by the liver which converts triglycerides into emulsified fat or small globules. Then these get converted into fatty acid and glycerol by the action of lipase.
Fatty acids, Glycerol and Monosaccharides are the end products of the fat digestion.
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