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Gerry Lennon
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Learning Outcomes1. Define homeostasis and explain its importance to
health
2. Identify the role of the nervous, endocrine andcirculatory systems in homeostasis
3. Describe the components of a feedback system
4. Compare positive and negative feedback loops andgive examples of each.
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Definition
Homeostasis is the bodys ability to maintain relatively stableinternal conditions even though the outside world iscontinuously changing
(Marieb, 2000)
The body is able to buffer fluctuations in the environmentwhich ensures cell functioning and ultimately survival.Changes include;
Nutrients eg.Glucose
Level of toxins/waste
Salinity (osmotic pressure)
WaterpHOxygenTemperature
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Why is homeostasis so important?
The body cells are extremely fussy about intracellularconditions (inside the cell) and it is the fluid outsidethe cell (extracellular/interstitial fluid) whichdetermines whether the inside of the cell is keptconstant. For continued health, chemical balance
must be maintained inside and outside of the cells
glucose carbondioxide
oxygen
ICF=Intracellular Fluid
cell
Extracellular
fluid (ECF)
ICF
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Maintenance of Homeostasis
Occurs via adaptive mechanisms under the control ofthe NERVOUS SYSTEM(neural responses) and theENDOCRINE SYSTEM(hormonal responses).
Neural and hormonal responses ensure that the
following are kept at optimum levels;
Body temperature
Blood pressure (BP)Balance of body salts (eg. NaCl)
Balance of O2 and CO2
Concentration of substance in blood eg. H2O
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Body Systems and Homeostasis
Practically everything that goes on in the body helpsmaintain homeostasis;
Kidneys removes a carefully regulated amount ofH2O and wastes
Lungs work with heart, blood vessels, blood todistribute O2and remove CO2
Digestive system- nutrients pass through the smallintestine into the blood and then to all body parts
Coordinated feedback mechanisms ensure thathomeostasis takes place and appropriate adaptationsby body made in response to changes or STRESSORS
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Imbalance
Most disease is seen as being due to the result ofhomeostasis being disturbed i.e. homeostaticimbalance
With increasing age the control systems are lessefficient and the stability of internal environment isweakened
Enabling Homeostasis to Occur
Need communication within the body: Nervous system - uses electrical & chemical
information that travels through nerves Endocrine system - uses hormones (chemicals
released from endocrine organs) which travel in thebloodstream to their target areas
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The Control SystemReceptor
Is a sensor that monitors the environment andresponds to the change (stimuli)
The control centre
Determines the set point i.e. the range or level at
which the variable has to be maintained Information is now analyzed and an appropriate
response
The effector
This provides the way that something can happen The results then get fed back to influence the stimulus
so that it is repressed/ reduced (negative feedback) orenhanced (positive feedback)
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Variables such astemperature, blood
sugar, and BP areregulated by the bodysresponse to deviationsaway from the norm
and which is calledHomeostasis.Changes in a variablewill stimulate a
receptor to sendmessages to the brainor control centre whichtriggers a response tobring it back to normal
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Negative Feedback
The variable changes in a direction OPPOSITE to thatof the initial change returning it to its ideal value
The output of the system shuts off the original
stimulus or reduces its intensity
The endocrine, cardiovascular and neurologicalsystem are all important for this process
One example is that of temperature control
Can you think of any others?
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Example of Negative Feedback
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Positive Feedback The result or response ENHANCES OR
EXAGGERATES the original stimulus so that theactivity (output) is accelerated
It is positive as the change that occurs is in the SAMEdirection as the initial disturbance and so the variable
deviates further and further from its original value orrange
They control infrequent events that do not needcontinuous adjustments
Amplifies something and usually triggers a cascadesystem
Example: clotting cascade and contractions whengiving birth
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Types of Stressors Affecting
Homeostasis Physical: heat, noise
Chemical: food, hormones
Microbiological: viruses, bacteria
Physiological: tumour
Developmental: age, genetic factors
Psychological: emotional and mental disturbances.
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Illness and DeathIf all systems are functioning adequately thenhomeostasis can be restored quickly via the feedbackmechanisms.
If a system breaks down then person may feel ill.When the body is unable to restore homeostasis thenexternal interventions may be required in order to avoidor delay death.
Can you suggest such interventions you may have seenin clinical practice?
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Group Work!
1. Split into groups of three and identify yourselves as A, B or C
2. Those who are As should explain the components includedin a homeostatic feedback system and how it works- trydrawing a diagram to help you.
3. Those who are Bs need to give an example of a negativefeedback mechanism in our body and describe how it works
including stating where the control centre is located.(choose a simple example!)
4. Finally, those of you who are the Cs need to give an exampleof a positive feedback mechanism, and explain why this isnot as common as negative feedback systems. (you do not
need to explain the detail of your example)
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