Thermodynamics, the science of energy interactions, governs the direction of processes found in nature. While the subject finds wide applications in science and technology, its connection to biological sciences and in particular to bio-engineering is becoming increasingly important. In this work, after a brief introduction to the fundamental concepts in thermodynamics, we focus on its application in human physiology. A review of application of thermodynamics to the interaction between human body and environment is presented. Research works on biological systems such as the nervous system and the cardiovascular systems are summarized. The thermodynamics of metabolism is reviewed, and finally, the role of the subject in understanding and combating diseases is highlighted.