Control of the Internal Environment

Chapter 2

Homeostasis: Dynamic Constancy Homeostasis

– Maintenance of a constant or unchanging “normal” internal environment

– Few / mild demands so few responses

Homeostasis: Dynamic Constancy Steady state

– Constant internal environment, but not necessarily “normal”

– Balance achieved between demands placed on body and the response to those demands

Some Examples:

Changes in Blood Pressure at Rest

Changes in Body Core Temperature During Exercise

What controls the system?

Biological Control Systems

Series of interconnected components that serve to maintain a physical or chemical parameter near normal

Receptor– Capable of detecting changes

Integrating center– Assesses input and initiates response

Effector– Corrects changes to internal environment

Nature of Control Systems

Most control systems act via negative feedback– Response reverses the initial disturbance

in homeostasis

Components of a Biological Control System

Regulation of Room Temperature: a Non-Biological Control System

Example of Homeostatic Control:Regulation of Blood Pressure

Stimulus– Increased blood pressure from HR

Receptors – Baroreceptors in carotid arteries and aorta

Integrating center – Medulla of the brain

Effector – Heart

Response– Decreased blood pumped from heart

Example of Homeostatic Control:Regulation of Blood Pressure

Example of Homeostatic Control:Regulation of Blood Glucose

Nature of Control Systems

Gain of the system– Degree to which the control system

maintains homeostasis– System with large gain is more capable of

maintaining homeostasis• Large gain = narrow limits• Small gain = wide limits

Example of Homeostatic Control:Regulation of Blood Glucose

Questions?

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