(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.

LECTURE 1Control of the Internal Environment

PHYSIOLOGY OF PHYSICAL ACTIVITIES

Adapted from

Theory and Application to Fitness and Performance, 5th edition

Scott K. Powers & Edward T. HowleyPresentation revised and updated byMOHD SANI MADON (PhD)

UPSI 2011

(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.

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

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Homeostasis: Dynamic Constancy

Homeostasis Maintenance of a constant internal

environment

Steady state Balance between demands placed on

body and the physiological response to those demands

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Body Core Temperature During Exercise

Fig 2.2

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Blood Pressure at Rest

Fig 2.3

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Control Systems of the Body

Goal To regulate some physiological variable

at or near constant value

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Non-Biological Control System in roomTemperature below 200 C

Thermostat set at 200 C

Heating System

Room temperature

Returns to 200 C

Room TemperatureSignals thermostat

To turn off heat

Fig 2.4

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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

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Components of a Biological Control System

Fig 2.5

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Negative Feedback

Most biological control systems Response reverses the initial disturbance

in homeostasis

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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

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Example:Regulation of Blood Pressure

Fig 2.6

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Example:Regulation of Blood Glucose

Fig 2.7

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Example:Cellular Stress Response

Fig 2.8

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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