Glycogenesis and Glycogenolysis

Glycogenesis

• Definition: Formation of glycogen from glucose monomers.
• Condition: Occurs when glucose levels in the blood exceed the needs for ATP production.
• Purpose: Stores energy from excess nutrients.
• Location: Primarily in the liver and skeletal muscle.
• Hormonal Influence: Insulin signals liver cells (hepatocytes) to store glucose as glycogen.
• Key Intermediate: Glucose 6-phosphate.
• Key Enzyme: Glycogen synthase.

Glycogenolysis

• Definition: Breakdown of glycogen.
• Condition: Triggered by low blood sugar levels.
• Key Enzyme: Glycogen phosphorylase.
• Hormonal Influence:
  • Stimulated by glucagon and cortisol (stress hormone).
  • Occurs mainly in the liver, but also in kidney and intestinal cells.
• Energy Storage: Complex carbohydrates (like glycogen) have more energy than proteins.

Carbohydrate Loading

• Strategy: High carbohydrate diet for 3-4 days with reduced physical activity.
• Purpose: Enhances performance and endurance by increasing glycogen stores.
• Comparison with Protein: Carbohydrates are more efficient for short-term energy needs compared to protein.

Gluconeogenesis

• Definition: Formation of new glucose from non-carbohydrate sources.
• Condition: Occurs when blood glucose levels drop to prevent hypoglycemia.
• Key Substrates:
  • Glycerol
  • Amino acids
  • Glycolysis intermediates
• Importance: Essential for glucose-dependent tissues like the nervous system.
• Hormonal Influence:
  • Stimulated by cortisol, glucagon, and epinephrine.
  • Hormones create a synergistic effect, enhancing glucose production more than their additive effects.

Synergistic Hormonal Effects

• Explanation:
  • Instead of a simple sum of effects, the combination of hormones like cortisol, glucagon, and epinephrine amplifies the response.
  • Example: Individually, each hormone may increase glucose by 1 unit, but together they may increase it by 5 units.