The science of physiology overlaps with chemistry and physics, and shares knowledge with the related sciences of pathophysiology and comparative physiology. Pathophysiology is concerned with the functions of diseased or injured body systems and is based on knowledge of how normal systems function, which is the focus of physiology. All of the information in this book has been gained by applications of the scientific method. This method has three essential characteristics. It is assumed that the subject under study can ultimately be explained in terms we can understand.
Homeostasis refers to the dynamic constancy of the internal environment.
Homeostasis is maintained by mechanisms that act through negative feedback loops. In a negative feedback loop the effector acts to cause changes in the internal environment that compensate the initial deviations that were detected by the sensor. The nervous and endocrine systems provide extrinsic regulation of other body systems and act to maintain homeostasis. The secretion of hormones is stimulated by specific chemicals and is inhibited by negative feedback mechanisms. Effectors act antagonistically to defend the set point against deviations in any direction.