Metabolism

The whole range of biochemical processes that occur within us (or any living organism). Metabolism consists both of anabolism and catabolism (the buildup and breakdown of substances, respectively). The term is commonly used to refer specifically to the breakdown of food and its transformation into energy.

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1. The sum of the chemical and physical changes occurring in tissue, consisting of anabolism, those reactions that convert small molecules into large, and catabolism, those reactions that convert large molecules into small, including both endogenous large molecules as well as biodegradation of xenobiotics. 2. Often incorrectly used as a synonym for either anabolism or catabolism. [G. metabole, change]

- basal m. oxygen utilization of an individual during minimal physiologic activity while awake; an obsolete test determined by measuring oxygen consumption of a fasting subject at complete bodily and mental rest and a room temperature of 20°C. SYN: basal metabolic rate.

- carbohydrate m. oxidation, breakdown, and synthesis of carbohydrates in the tissues.

- electrolyte m. the chemical changes that various essential minerals ( e.g., sodium, potassium, calcium, magnesium) undergo in the tissues.

- energy m. those metabolic reactions whose role is to release or to provide energy.

- fat m. oxidation, decomposition, and synthesis of fats in the tissues.

- first-pass m. the intestinal and hepatic degradation or alteration of a drug or substance taken by mouth, after absorption, removing some of the active substance from the blood before it enters the general circulation. SYN: first-pass effect.

- inborn error of m. a genetic biochemical disorder of a specific enzyme that forms a metabolic block, e.g., phenylketonuria.

- intermediary m. the sum of all metabolic reactions between uptake of foodstuffs and formation of excretory products.

- oxidative m. SYN: ventilation (2).

- primary m. metabolic processes central to most cells; e.g., biosynthesis of macromolecules, energy production, turnover, etc.

- protein m. decomposition and synthesis of protein in the tissues. SYN: proteometabolism.

- respiratory m. the exchange of respiratory gases in the lungs, oxidation of foodstuffs in the tissues, and production of carbon dioxide and water.

- secondary m. metabolic processes in which substances (such as pigments, alkaloids, terpenes, etc.) are only synthesized in certain types of tissues or cells or are only synthesized under certain conditions.

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me·tab·o·lism mə-'tab-ə-.liz-əm n

1 a) the sum of the processes in the buildup and destruction of protoplasm specif the chemical changes in living cells by which energy is provided for vital processes and activities and new material is assimilated <methods of determining body and tissue \metabolism (Bull. of the Univ. of Ky.)> see ANABOLISM, CATABOLISM

b) the sum of the processes by which a particular substance is handled (as by assimilation and incorporation or by detoxification and excretion) in the living body <the \metabolism of iodine in the thyroid>

2) METAMORPHOSIS (2) usu. used in combination <holometabolism>

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n.

1. the sum of all the chemical and physical changes that take place within the body and enable its continued growth and functioning. Metabolism involves the breakdown of complex organic constituents of the body with the liberation of energy, which is required for other processes (see catabolism) and the building up of complex substances, which form the material of the tissues and organs, from simple ones (see anabolism). See also basal metabolism.

2. the sum of the biochemical changes undergone by a particular constituent of the body; for example, protein metabolism.

• metabolic adj.

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me·tab·o·lism (mə-tabґə-liz″əm) [Gr. metaballein to turn about, change, alter] 1. the sum of all the physical and chemical processes by which living organized substance is produced and maintained (anabolism), and also the transformation by which energy is made available for the uses of the organism (catabolism). 2. biotransformation.