This textbook explores the fundamental qualitative and quantitative aspects of human physiology. It approaches biological and physiological processes and phenomena from a quantitative perspective, revealing how physiological problems can be mathematically formulated starting from simple laws of physics. The book addresses a broad range of topics, including: the statics and dynamics of circulation; muscle and sarcomere force-length and force- velocity relations, together with their mechanisms and functional consequences; subdivisions and meaning of the heat produced by muscle; locomotion, statics and dynamics of respiration; diffusion of gases and acid base equilibrium; phonation; general functions of the kidney and of the different sections of the nephron; changes in