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By studying this chapter, you should be able to do the following:

  1. Define the terms homeostasis and steady state.

  2. Diagram and discuss a biological control system.

  3. Give an example of a biological control system.

  4. Explain the term negative feedback.

  5. Define what is meant by the gain of a control system.

  6. Discuss the concept of hormesis and exercise.

  7. Identify five cell signaling mechanisms.

  8. Define heat shock proteins and explain how these proteins protect cells against damage.


Homeostasis: Dynamic Constancy

Control Systems of the Body

Nature of the Control Systems

  • Negative Feedback

  • Positive Feedback

  • Gain of a Control System

Examples of Homeostatic Control

  • Regulation of Body Temperature

  • Regulation of Blood Glucose

Exercise: A Test of Homeostatic Control

Exercise Improves Homeostatic Control via Cellular Adaptation

Stress Proteins Assist in the Regulation of Cellular Homeostasis

Key Terms



autocrine signaling

biological control system

cell signaling

control center


endocrine signaling

endocrine system


heat shock proteins



intracrine signaling

juxtacrine signaling

negative feedback

paracrine signaling


steady state

stress proteins

More than 100 years ago, the French physiologist Claude Bernard observed that the “milieu interior” (internal environment) of the body remained remarkably constant despite a changing external environment (see A Look Back—Important People in Science). The fact that the body maintains a relatively constant internal environment in spite of stressors (e.g., heat, cold, exercise) is not an accident but is the result of many control systems (16). Control mechanisms that are responsible for maintaining a stable internal environment constitute a major chapter in exercise physiology, and it is helpful to examine their function in light of simple control theory. Therefore, this chapter introduces the concept of “control systems” and discusses how the body maintains a relatively constant internal environment during periods of stress.

A LOOK BACK—IMPORTANT PEOPLE IN SCIENCE Claude Bernard—A Founding Father of Physiology


Boyer/Roger Viollet/Getty Images

Claude Bernard (1813–1878) was a French physician and physiologist. Importantly, Bernard is considered one of the founding “fathers of physiology.” Indeed, Dr. Bernard’s research and writings greatly improved our understanding of physiology during the nineteenth century, and he is credited with recognizing the importance of a constant internal environment. A brief overview of Dr. Bernard’s life and contributions to physiology follows.

Claude Bernard was born in the French village of Saint-Julien and received his early education at the local Jesuit school. He attended Lyon College briefly, but left college to devote his efforts toward becoming a successful writer. At the age of 21, Dr. Bernard went to Paris to formally launch his writing career. However, following discussions with literature critics, Dr. Bernard abandoned writing and decided to study medicine as a career. As a medical intern at a Paris hospital, Dr. Bernard began to work with a senior French physician/physiologist, Francois Magendie, who was involved in research and teaching medical students. Dr. Bernard quickly became Magendie’s ...

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