Biochemistry · MU Pleven

23. Regulation of Carbohydrate Metabolism. Control of Blood Glucose Level in Different Conditions: well Fed State, Fasting, Prolonged Starvation. Metabolic disturbance in Diabetes Mellitus.

Covers how carbohydrate metabolism is regulated by insulin, glucagon, epinephrine, cortisol and growth hormone, and the key control enzymes of glycolysis, gluconeogenesis and glycogen metabolism. It then walks through blood glucose control in the well-fed state, short fasting, and prolonged starvation with ketone body production, before describing the metabolic disturbances of Type 1 and Type 2 diabetes mellitus and their long-term complications.

Inside: 5 sections · 8 labelled pictures · 20 flashcards · 3 min

Topic 23 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 5 sections, about 408 words (3 min of reading), with 20 flashcards.

In this note

  1. Regulation of Carbohydrate Metabolism.
  2. Regulation of Carbohydrate Metabolism
  3. Control of Blood Glucose Levels in Different States
  4. Prolonged Starvation (1–2 days and beyond)
  5. Metabolic Disturbances in Diabetes Mellitus

Regulation of Carbohydrate Metabolism

  • Carbohydrate metabolism is regulated to maintain stable blood glucose, ensure energy supply, and coordinate use vs. storage of nutrients.
  • Key regulatory hormones:
  • Insulin → promotes storage and utilization of glucose.
  • Glucagon → promotes glucose release from stores.
  • Epinephrine → rapid glucose release during stress/exercise.
  • Cortisol and Growth Hormone → increase blood glucose during prolonged stress and fasting.
  • Main control points in pathways:
  • Glycolysis: key regulatory enzymes
  • Hexokinase/Glucokinase
  • Phosphofructokinase-1 (PFK-1)
  • Pyruvate kinase
  • Gluconeogenesis:
  • Pyruvate carboxylase
  • PEP carboxykinase
  • Fructose-1,6-bisphosphatase
  • Glycogen metabolism:
  • Glycogen synthase (storage)
  • Glycogen phosphorylase (breakdown)
  • Insulin decreases blood glucose by:
  • ↑ Glucose uptake (GLUT4) in muscle and adipose
  • ↑ Glycolysis
  • ↑ Glycogenesis
  • ↑ Lipogenesis
  • Inhibits gluconeogenesis and glycogen breakdown
  • Glucagon increases blood glucose by:
  • ↑ Glycogenolysis (liver only)
  • ↑ Gluconeogenesis
  • ↓ Glycolysis (in liver)
  • ↑ Lipolysis → fatty acid oxidation → ATP to fuel gluconeogenesis

Control of Blood Glucose Levels in Different States

1. Well-fed State (After a Meal)

  • Hormone dominant: Insulin
  • Blood glucose ↑ due to digestion and absorption.
  • Metabolic responses:
  • Liver converts glucose → glycogen (glycogenesis).
  • Excess glucose → fatty acids → triglycerides storage.
  • Muscle stores glycogen and uses glucose for energy (glycolysis).
  • Adipose tissue forms fat from glucose.
  • Outcome: Blood glucose returns to normal (≈ 4.0–5.5 mmol/L).

2. Fasting State (4–18 hours after last meal)

  • Hormone dominant: Glucagon
  • Liver breaks down glycogen → glucose (glycogenolysis).
  • Gluconeogenesis begins (from lactate, amino acids, glycerol).
  • Fat breakdown ↑ → fatty acids used for energy by tissues.
  • Brain still requires glucose, not yet ketones.
  • Blood glucose remains stable despite no food intake.

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