Chapter 2 Control of the Internal Environment EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley

Objectives Define the terms homeostasis and steady state Diagram and discuss a biological control system Give an example of a biological control system Explain negative feedback Define what is meant by the gain of a control system

Homeostasis: Dynamic Constancy Maintenance of a constant internal environment Steady state Balance between the demands placed on a body and the physiological response to those demands

Body Core Temperature During Exercise Fig 2.2

Blood Pressure at Rest Fig 2.3

Control Systems of the Body Goal To regulate some physiological variable at or near constant value

Non-Biological Control System  in room Temperature below 200 C Room Temperature Signals thermostat To turn off heat Room temperature Returns to 200 C Thermostat set at 200 C Heating System Fig 2.4

Biological Control Systems Series of interconnected components that serve to maintain a physical or chemical parameter at or near constant Receptor Capable of detecting changes Integrating center Assesses input and initiates response Effector Corrects changes to internal environment

Components of a Biological Control System Fig 2.5

Negative Feedback Most biological control systems Response reverses the initial disturbance in homeostasis

Gain of a Control System Gain of the system Degree to which the control system maintains homeostasis System with large gain is more capable of maintaining homeostasis

Example: Regulation of Blood Pressure Fig 2.6

Example: Regulation of Blood Glucose Fig 2.7

Example: Cellular Stress Response Fig 2.8

Exercise: A Test of Homeostatic Control Submaximal exercise in a cool environment The body’s control systems can maintain steady state Maximal exercise or exercise in a hot/humid environment May not be able to maintain steady state Severe disturbances in homeostasis can occur

Chapter 2 Control of the Internal Environment