The sum of chemical and physical processes occurring within a living organism, but sometimes only used to refer to enzymic reactions. Consists of an alternation of anabolism (the build up and synthesis of complex molecules from simpler ones and the taking up and storing of energy) and catabolism (breaking them down with the release of energy). The synthesis and breakdown of the molecules or metabolites occur within a reaction sequence termed the metabolic pathway. Some pathways (e.g., glycosis) are linear, while others (the Krebs cycle) are cyclical. The term metabolic rate is often rather loosely associated with respiratory rate. Brain metabolism requires both oxygen and glucose, with oxygen metabolising glucose that in turn provides energy for living cells. While the brain represents about 2% of the body’s total weight, it nevertheless accounts for 20% of the body’s total oxygen use and 65% of its glucose needs. Gray matter of the brain, particularly the frontal lobes have the highest metabolic requirements, while the metabolic rates of the occipital, parietal, and temporal lobes together with the basal ganglia and cerebellum are lower, and the lowest metabolic need being a feature of the brain stem.
See Acetic acid, Basal ganglia (anatomy), Brain (or encephalon), Brain stem, Cerebellum (anatomy), Cortisol, Enzyme, Frontal cortex, Frontal lobes, Gray matter, Hormones, Iodine, Krebs cycle (or tri-carboxyclic acid, TCA, cycle), Mitochondria, Occipital cortex (or lobe), Parietal lobe, Purines, Pyrimidines, Temporal lobe