Metabolism is the set of chemical processes that sustain life by converting food and other substances into energy and the building blocks needed for growth, repair, and function. It encompasses all the reactions that occur inside cells, organized into two broad categories: catabolism and anabolism.

• Catabolism: the breakdown of large molecules (such as carbohydrates, fats, and proteins) to release energy and produce smaller molecules that fuel other processes.
• Anabolism: the constructive build-up of complex molecules (like proteins, nucleic acids, carbohydrates, and lipids) from smaller units, using energy.

Key points to know:

• Energy production: Metabolism powers every cellular activity, from muscle contraction to brain signaling, by producing adenosine triphosphate (ATP) and other energy carriers.
• Regulation: Metabolic pathways are tightly regulated by enzymes and by signals such as hormones, ensuring balance between energy intake, storage, and usage.
• Interconnectedness: Metabolic processes involve multiple organs and tissues (e.g., liver, muscles, fat tissue) and include digestion, respiration, and waste removal as integrated components of the overall metabolic system.
• Variability: Metabolic rate—the speed at which the body uses energy—varies among individuals and can be influenced by age, sex, body composition, genetics, activity level, and health status.

If you’d like, I can tailor this into a quick Glossary, or explain how metabolism changes with exercise, diet, or certain medical conditions.