Starch Digestion

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•  Processes occurring in the small intestine that result in the digestion of starch and transport of the products of

    digestion to the liver

Starch is a polysaccharide composed of glucose monomers and accounts for ~ 60% of the carbohydrates consumed by humans

  • Starch can exist in one of two forms – linear chains (amylose) or branched chains (amylopectin)

The digestion of starch is initiated by salivary amylase in the mouth and continued by pancreatic amylase in the intestines

  • Starch digestion by amylase does not occur in the stomach as the pH is unsuitable for amylase activity (optimal pH ~ 7)

Amylase digests amylose into maltose subunits (
disaccharide) and digests amylopectin into branched chains called dextrins

  • Both maltose and dextrin are digested by enzymes (maltase) which are fixed to the epithelial lining of the small intestine
  • The hydrolysis of maltose / dextrin results in the formation of glucose monomers

Glucose can be hydrolysed to produce ATP (cell respiration) or stored in animals as the polysaccharide glycogen

  • Glucose monomers can also be generated from the breakdown of other disaccharides (such as lactose and sucrose)

Overview of Starch Hydrolysis

starch hydrolysis

Role of Pancreas

The pancreas serves two functions in the breakdown of starch:

  • It produces the enzyme amylase which is released from exocrine glands (acinar cells) into the intestinal tract
  • It produces the hormones insulin and glucagon which are released from endocrine glands (islets of Langerhans) into the blood

The hormones insulin and glucagon regulate the concentration of glucose in the bloodstream (controls availability to cells)

  • Insulin lowers blood glucose levels by increasing glycogen synthesis and storage in the liver and adipose tissues
  • Glucagon increases blood glucose levels by limiting the synthesis and storage of glycogen by the liver and adipose tissues

Pancreatic Regulation of Glycogen Storage by the Liver

glycogen storage