Metabolism

Definition

Metabolism is the sum of all chemical reactions in the body that build (anabolism) or break down (catabolism) molecules to sustain life, produce energy, and eliminate waste.

Key Metabolic Pathways

• Glycolysis and gluconeogenesis (carbohydrate)
• Beta-oxidation (fat)
• Urea cycle (protein/nitrogen)
• Oxidative phosphorylation (energy)

Factors Affecting Metabolism

Thyroid hormone (most important regulator), age, body composition, physical activity, temperature, hormones, medications.

Liver's Role

Primary site of drug metabolism (Phase I: CYP450; Phase II: conjugation). Liver disease alters drug pharmacokinetics.

NCLEX Relevance

Hypothyroidism slows metabolism (cold intolerance, weight gain); hyperthyroidism increases it.