Metabolism encompasses the complex network of chemical reactions that sustain life within living organisms, enabling growth, reproduction, adaptation, and response to environmental changes. While some metabolic processes occur outside the cell, the majority take place intracellularly and are collectively known as intermediate metabolism. This book offers a structured and in-depth exploration of metabolic pathways, distinguishing clearly between anabolism, responsible for the biosynthesis of cellular components, and catabolism, which governs their degradation to release energy or generate metabolic intermediates. Particular emphasis is placed on the regulation of metabolism through integrated hormonal and nervous mechanisms, highlighting the central role of the autonomic nervous system and endocrine signaling in key metabolic organs such as the liver, muscles, and adipose tissue. By examining the interconnections between major biosynthetic and degradative pathways, the book elucidates essential reaction mechanisms, the functions of key coenzymes, and the pathological consequences arising from metabolic dysfunction. This work provides a solid academic foundation for students and researchers in biochemistry and related life sciences.