⚡️ 3. Glycogen is Stored in the Liver and Muscle

• Where is glycogen primarily stored in the body?

  Liver and muscle
• What can glucose be used for after absorption into a cell?

  Release energy or stored as glycogen
• What is glycogen?

  A large polymer of glucose
• Which cells can store large amounts of glycogen?

  Liver cells and muscle cells
• What percentage of their weight can liver cells store as glycogen?

  5 to 8 percent
• What percentage of their weight can muscle cells store as glycogen?

  1 to 3 percent
• What is the average molecular weight of glycogen?

  5 million or greater
• Why is glycogen stored as a high-molecular-weight compound?

  To avoid altering osmotic pressure significantly
• What would happen with high concentrations of low-molecular-weight monosaccharides?

  They would disrupt osmotic relations
• What is glycogenesis?

  • Formation of glycogen from glucose
  • Involves conversion of glucose-6-phosphate to glucose-1-phosphate
  • Requires specific enzymes
  • Other compounds can also be converted to glucose
• What is the first step in glycogenesis?

  Conversion of glucose-6-phosphate to glucose-1-phosphate
• What can enter the reactions of glycogenesis?

  Any monosaccharide convertible to glucose
• What is glycogenolysis?

  Breakdown of stored glycogen to glucose
• How does glycogenolysis occur?

  By phosphorylation, not reversal of glycogenesis
• What enzyme catalyzes the breakdown of glycogen?

  Phosphorylase
• What is the state of phosphorylase under resting conditions?

  It is in an inactive form
• How is phosphorylase activated?

  By hormones like epinephrine or glucagon
• How do epinephrine and glucagon activate phosphorylase?

  • Promote formation of cyclic AMP
  • Initiate a cascade of reactions
  • Activate phosphorylase for glycogen breakdown
• What triggers the release of epinephrine?

  Stimulation of the sympathetic nervous system
• What is one function of epinephrine in the body?

  Increase availability of glucose for energy
• What cells does epinephrine affect significantly?

  Liver cells and muscle cells
• What does glucagon do when blood glucose is low?

  Stimulates conversion of liver glycogen to glucose
• What cells secrete glucagon?

  Alpha cells of the pancreas
• What is the effect of glucagon on blood glucose concentration?

  It elevates blood glucose concentration
• What is the role of glucagon in blood glucose regulation?

  • Secreted when blood glucose is low
  • Stimulates liver glycogen conversion to glucose
  • Elevates blood glucose levels