This literary work serves as an introductory primer to the vast array of structures and functions that exist within the organ and tissue systems of animals. This book delves into the concepts and processes that keep life going and the body in a constant state of equilibrium. It covers topics including water and gas exchange, nutrition and oxygen acquisition and transport, temperature control, the transmission of electrical and chemical signals, sensory processing, and movement. The study of animal physiology centres on the operations of multicellular organisms' tissues, organs, and organ systems. With the aim of comprehending the operational mechanisms of living organisms across all levels, from subcellular to the integrated whole organism, animal physiologists endeavour to establish physical and chemical references. To comprehend the inner workings of animals, one must be well-versed in the complex chemical relationships that initiate cellular activities. Animal physiologists utilise this information to formulate hypotheses and orchestrate experiments in order to gain insights into the regulation and control of processes occurring within cellular clusters, as well as the subsequent impact of the collective activities of these cellular clusters on the overall functionality of the animal. The specialised organs comprised of coordinated cell activities serve as the foundation for the physiological processes and behavioural capabilities that differentiate animals from plants. Prominent characteristics encompass, but are not limited to, locomotion, considerable autonomy from environmental factors, intricate sensory perception of the surroundings, and formidable social engagements.