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The Digestive System 1

Lab # 8. The Digestive System 1 . Digestion has two facets:. 1- Mechanical digestion . It is the physical breakdown of food into smaller particles. Mechanical digestion exposes more food surface to the action of digestive enzymes and is achieved by:.

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The Digestive System 1

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  1. Lab # 8 The Digestive System 1

  2. Digestion has two facets: 1- Mechanical digestion It is the physical breakdown of food into smaller particles Mechanical digestion exposes more food surface to the action of digestive enzymes and is achieved by: • - Cutting and grinding action of the teeth • - Churning action of stomach and small intestines 2- Chemical digestion It is a series of hydrolysis reactions that breaks dietary macromole-cules into their monomers: • Polysaccharides monosaccharides • Proteins amino acids • Fats monoglycerides and fatty acids • Nucleic acids nucleotides • Chemical digestion is carried out by digestive enzymes produced by salivary glands, stomach, pancreas and small intestine.

  3. 1- Carbohydrates Polysaccharides Starch is the most digestible carbohydrate • Cellulose and chitin are indigestible Monosaccharides Digestion

  4. Amylases Amylases Amylases Disaccharides Monosaccharides Starch is the most digestible carbohydrate • They are absorbed immediately 2- Proteins Oligosaccharides Proteases Peptidases Protein Aminoacids Ex: Pepsin Polypeptides • They are absorbed immediately

  5. 3- Lipids + Lipases Triglycerides Glycerol Fatty acids Lipases + Monoglycerides Fatty acids

  6. Monosaccharides + Amylase + Benedict’s reagent + Lugol’s reagent Starch Dark blue color Greenish-brownish precipitate

  7. Test Protein Digestion Pepsin (active enzyme) Parietal cells HCl Partially digested proteins Pepsinogen (zymogen) + Biuret reagent Chief cells Lavender-pink color Removed peptide

  8. Test Lipid Digestion Hydrophobic quality of lipids makes their digestion and absorption more complicated that carbohydrates and proteins Enzymes that digest lipids (fats) are called lipases • The lingual lipase secreted by the intrinsic salivary glands of the tongue is active in mouth, but more active in stomach along with gastric lipase. 10-15% of lipids digested before reaches duodenum • Pancreatic lipase in the small intestine digest most of the fats 1- Emulsification Components of the bile Fat globule is broken up and coated by lecithin and bile acids. Emulsification droplets

  9. 2- Fat Hydrolysis • Pancreatic lipase acts on triglycerides. It removes the first and third fatty acids from glycerol backbone and leaves the middle one • The product of lipase action are two free fatty acids (FFAs) and a monoglyceride Emulsification droplets are acted upon by pancreatic lipase, which hydrolyzes the first and third fatty acids from triglycerides usually leaving the middle fatty acid. Pancreatic lipase Free fatty acid pH

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