Biochemical Foundations of Human Vital Activity - Volkov, N. I., & Nesen, E. N. 2000

Biochemical Foundations of Human Vital Activity
Metabolism in the Organism
Metabolism is an essential condition for the existence of a living organism

The Human Body is inextricably linked with the external environment. Throughout life, nutrients (CARBOHYDRATES, fats, Proteins), along with other organic and Mineral Substances—including Water and oxygen—enter the body from the outside. They are utilized either to build the body’s own structures or to generate energy. Metabolic waste products and a portion of energy, primarily in the form of heat, are released from the body into the environment (Fig. 6).

Over 40 years of life, an adult consumes tons of nutrients and drinks about 20,000 liters of water without any change in body weight. This indicates that the body, functioning as an open system—that is, interacting with the environment—is capable of establishing and maintaining a constant chemical composition within its internal environment, known as Homeostasis. This fundamental property of a living Organism ensures its self-renewal and self-preservation, which is made possible by the continuous process of METABOLISM.

Metabolism refers to the strictly ordered system of biochemical and physiological processes that ensure the intake of nutrients and other substances into the body, their assimilation and intracellular transformation, as well as The excretion of metabolic end products into the external environment.

Metabolism drives GROWTH AND DEVELOPMENT, the self-renewal of all cellular structures, the energy supply for physiological Functions, the maintenance of internal homeostasis, ADAPTATION TO ENVIRONMENTAL stressors (including physical exertion), and other vital life processes. Consequently, the cessation of metabolism disrupts or terminates life itself.

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Fig. 6 Diagram of Metabolism in the Body

A key feature of metabolic processes in a living organism is their high reaction rate, which is driven by biological catalysts known as Enzymes. Cells contain complex enzyme systems whose actions are often interconnected in such a way that the product of one enzymatic reaction serves as the substrate for another. This forms intricate metabolic pathways for The conversion of various substances, leading to The breakdown of complex molecules into simpler ones or the synthesis of complex proteins and other macromolecules.

A metabolic pathway is a sequence of Chemical Reactions Involving numerous enzymes (E) that progressively convert substances into corresponding end products (P). Metabolic pathways are classified into linear and cyclic types:

Substances formed during metabolic reactions (B, C, D, P) are called metabolites. Integrating chemical reactions into metabolic cycles enables the self-Regulation of Metabolic pathways by the final reaction product, as well as the interconnection and INTEGRATION OF METABOLIC processes across different classes of substances.

The central metabolic pathway in the human body is the aerobic oxidation of glucose, which involves the gradual breakdown of a glucose molecule into pyruvic acid and subsequently into acetyl-CoA, followed by oxidation in The Citric Acid Cycle to the final metabolic products C0₂ and H₂O. This pathway acts as a convergence point for numerous other nutrient conversion processes accompanied by the release of Free energy. Subsequent chapters will examine only the principal metabolic pathways that provide the energy required for muscular activity, recovery processes, and the body's adaptation to physical exertion.

Metabolic processes are characterized by strict Organization and coordination. This is achieved both through the action of enzymes and their precise spatial arrangement within cellular structures, as well as through The Influence of various regulatory mechanisms.