Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Metabolism and Energy
Basic Concepts

METABOLISM and Energy transformation constitute a fundamental characteristic shared by All living organisms. Substances from the external environment continuously enter The Human Body. Specifically, nutrients (Proteins, fats, CARBOHYDRATES), Vitamins, Water, and mineral salts are introduced via the Digestive System. Atmospheric oxygen enters the bloodstream through the Lungs and, to a lesser extent, the Skin. Carried by the Blood flow, these substances are delivered to Cells and Tissues. Various biochemical processes take place within the Cytoplasm and Organelles of the body's cells, during which the incoming substances undergo transformation and are consumed for specific purposes (such as energy production). These processes can yield both beneficial and harmful byproducts, the latter of which must be expelled into the external environment. Waste products are eliminated by the Kidneys, lungs, and to a lesser extent, the skin and gastrointestinal tract.

Metabolism (energy and material exchange) is the ensemble of physiological processes designed to supply the body with the substances essential for its vital activity, transform and utilize them to generate energy and build cellular structures, and ultimately remove the unnecessary byproducts of these reactions into the external environment. In a narrower sense, metabolism refers to the pathways by which a specific substance (or substances) is transformed within the Organism (e.g., glucose metabolism).

Synthesis and Breakdown processes constantly occur within the body's various structures. Specifically, cells synthesize A wide variety of substances used to build and renew Cell membranes and organelles. The synthesis of new substances proceeds with an expenditure of energy and requires raw Materials, which either enter the body with food or are generated through The breakdown of older structures. Reactions directed toward the synthesis of new molecules are called anabolic. The component of metabolism that encompasses all anabolic reactions taking place in the body is referred to as plastic metabolism (anabolism, or assimilation).

Energy is required to drive the processes of plastic metabolism. It is generated through the breakdown of complex organic molecules (proteins, fats, carbohydrates) into simpler components, ultimately yielding water and carbon dioxide. Breakdown reactions accompanied by the release of energy are called catabolic. Together, all catabolic reactions constitute Energy Metabolism (Catabolism, or dissimilation). All reactions of plastic and energy metabolism are mediated by biological catalysts known as Enzymes.

Thus, metabolism comprises two directly opposing processes: anabolism and catabolism. They continually transition into one another and occur concurrently throughout the organism's entire life span. The predominance of one over the other leads to corresponding shifts in metabolism. Enhanced assimilation drives GROWTH AND DEVELOPMENT in the body. Conversely, when dissimilation reactions prevail, structural cellular elements undergo active degradation, leading to physical depletion and Aging. In childhood, plastic metabolism reactions predominate. As the organism ages, The Role of catabolic processes increases, and the synthesis of new substances is gradually suppressed.