Homeostasis

Homeostasis

Homeostasis is the maintenance of a stable internal environment.

Homeostasis

Homeostasis represents a state of DYNAMIC EQUILIBRIUM.

Homeostasis

Homeostasis represents a state of DYNAMIC EQUILIBRIUM.

This means that adjustments are always being made to keep the variables within an acceptable range.

Homeostasis

Homeostasis

All homeostatic mechanisms involve three components:

Homeostasis

All homeostatic mechanisms involve three components:1. Receptors (sensors)

Monitors the environment & responds to a stimulus

Homeostasis

All homeostatic mechanisms involve three components:1. Receptors (sensors)

Monitors the environment & responds to a stimulus Transmits the stimulus (information) to a control

center along a afferent pathway

Homeostasis

All homeostatic mechanisms involve three components:2. Control Center

Determines the “set points” or range to be maintained

Homeostasis

All homeostatic mechanisms involve three components:2. Control Center

Determines the “set points” or range to be maintained

Establishes the type of response

Homeostasis

All homeostatic mechanisms involve three components:2. Control Center

Determines the “set points” or range to be maintained

Establishes the type of response Sends this information though a Efferent Pathway

Homeostasis

All homeostatic mechanisms involve three components:3. Effector

Mechanism for controlling the variable or response

Homeostasis

All homeostatic mechanisms involve three components:3. Effector

Mechanism for controlling the variable or response

A reduced response is called a NEGATIVE FEEDBACK

Homeostasis

All homeostatic mechanisms involve three components:3. Effector

Mechanism for controlling the variable or response

A reduced response is called a NEGATIVE FEEDBACK

An increase in response is a POSITIVE FEEDBACK

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Figure 1.4 Interaction among the elements of a homeostatic control system.

Stimulusproduceschange invariable.

Receptordetects change.

Input: Information sent along afferent pathway to control center.

Output:Information sent along efferent pathway to effector.

Responseof effector feeds back to reduce the effect ofstimulus and returns variable to homeostatic level.

Receptor Effector

ControlCenter

1

2

34

5

BALANCE

Afferentpathway

Efferentpathway

Homeostasis

Negative Feed Back is the major mechanism for controlling homeostatic responses.

Homeostasis

Negative Feed Back is the major mechanism for controlling homeostatic responses.

The stimulus is either turned off or reduced in its intensity

Homeostasis

Consider body temperature:

Temperature change in the body is the variable

Homeostasis

Consider body temperature:

Temperature change in the body is the variable The change in temperature up or down is the response

Can you think of any other examples?

Copyright © 2010 Pearson Education, Inc.

Figure 1.5 Regulation of body temperature by a negative feedback mechanism.

Sweat glands activated

Shiveringbegins

StimulusBody temperaturerises BALANCE

Information sentalong the afferentpathway to controlcenter

Information sentalong the afferentpathway to controlcenter

Afferentpathway

Afferentpathway

Efferentpathway

Efferentpathway

Information sentalong the efferentpathway toeffectors

Information sentalong the efferentpathway to effectors

StimulusBody temperature falls

ReceptorsTemperature-sensitivecells in skin and brain

ReceptorsTemperature-sensitivecells in skin and brain

EffectorsSweat glands

EffectorsSkeletal muscles

Control Center(thermoregulatory

center in brain)

Control Center(thermoregulatory

center in brain)

ResponseEvaporation of sweatBody temperature falls;stimulus ends

ResponseBody temperature rises;stimulus ends

Homeostasis

Positive Feed Back is a minor mechanism for controlling homeostatic responses and is used for only occasional events.

The stimulus goes in the same direction as the response. One increases the other increases.

Can you think of any examples?

Homeostasis

Blood Clotting and Labor Contractions

Homeostasis

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Figure 1.6 Summary of the positive feedback mechanism regulating formation of a platelet plug.

Feedback cycle endswhen plug is formed.

Positive feedbackcycle is initiated.

Positivefeedbackloop

Break or tearoccurs in blood vessel wall.

Plateletsadhere to site and release chemicals.

Released chemicals attract more platelets.

Platelet plugforms.

2

1

3

4

Homeostasis

Disease occurs when the homeostatic mechanisms fail or are overwhelmed.Examples include:

Heart Failure Anaphylaxis Diabetes Hemophilia

Congested Heart Failure

Anaphylaxis

Anaphylaxis

Anaphylaxis

Diabetes

Homeostasis

How about a cold or flu?

How about cancer?