Greek: ἁνά, "upward" and βάλλειν, "to throw") is the set of
metabolic pathways that construct molecules from smaller units.
 These reactions require
energy, known also as an
endergonic process. One way of categorizing
metabolic processes, whether at the
cellular, organ or organism level, is as "anabolic" or as "
catabolic", which is the opposite and thus the separation of a macromolecule. Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in
cellular respiration. Many anabolic processes are powered by the
hydrolysis of adenosine triphosphate (ATP).
Anabolic processes tend toward "building up"
tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves
synthesis of complex
molecules. Examples of anabolic processes include the growth and mineralization of
bone and increases in
Endocrinologists have traditionally classified
hormones as anabolic or catabolic, depending on which part of metabolism they stimulate. The classic anabolic hormones are the
anabolic steroids, which stimulate protein synthesis, muscle growth, and
 The balance between anabolism and catabolism is also regulated by
circadian rhythms, with processes such as glucose metabolism fluctuating to match an animal's normal periods of activity throughout the day.