Metabolism Associated Diseases and Disorders
Metabolic physiology encompasses the biochemical processes that maintain life, including the conversion of nutrients into energy, the synthesis of essential molecules, and the elimination of waste products. It involves a complex network of pathways regulated by enzymes, hormones, and signaling molecules to ensure cellular and systemic energy homeostasis.
1. Types of Metabolism
• Catabolism – Breakdown of molecules to release energy (e.g., glycolysis, fatty acid oxidation).
• Anabolism – Synthesis of complex molecules from simpler precursors (e.g., protein synthesis, glycogenesis).
• Amphibolic Pathways – Serve both anabolic and catabolic functions (e.g., citric acid cycle).
2. Major Metabolic Pathways
• Glycolysis – Converts glucose to pyruvate with net ATP production.
• Citric Acid Cycle – Oxidizes acetyl-CoA to CO₂, producing NADH and FADH₂ for ATP generation.
• Oxidative Phosphorylation – Uses electron transport chain to generate ATP via chemiosmosis.
• Gluconeogenesis – Synthesizes glucose from non-carbohydrate precursors.
• Lipolysis – Breakdown of triglycerides into glycerol and fatty acids.
• β-Oxidation – Breaks down fatty acids into acetyl-CoA for energy.
• Amino Acid Metabolism – Deamination, transamination, and conversion to metabolic intermediates.
3. Hormonal Regulation of Metabolism
| Hormone | Metabolic Role | Effect |
| Insulin | Promotes glucose uptake, glycogen synthesis, lipogenesis, protein synthesis. | Lowers blood glucose; anabolic effects. |
| Glucagon | Stimulates glycogenolysis, gluconeogenesis, lipolysis. | Raises blood glucose; mobilizes energy stores. |
| Cortisol | Stimulates gluconeogenesis, protein breakdown, lipolysis. | Supports stress response; increases blood glucose. |
| Epinephrine | Activates glycogenolysis, lipolysis; increases metabolic rate. | Prepares body for ‘fight or flight’. |
| Thyroid Hormones (T3, T4) | Increase basal metabolic rate and stimulate macronutrient metabolism. | Enhance oxygen consumption and thermogenesis. |
4. Energy Balance
Energy balance is achieved when caloric intake matches energy expenditure. Positive energy balance leads to storage of excess energy as fat, while negative energy balance results in weight loss. Basal metabolic rate (BMR), physical activity, and thermic effect of food determine total daily energy expenditure.
5. Disorders of Metabolism
• Diabetes Mellitus – Impaired insulin production or action leading to chronic hyperglycemia.
• Metabolic Syndrome – Cluster of metabolic abnormalities increasing cardiovascular risk.
• Hypothyroidism/Hyperthyroidism – Altered thyroid hormone levels affecting metabolic rate.
• Inborn Errors of Metabolism – Genetic enzyme deficiencies disrupting specific metabolic pathways.