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HomeostasisChapter 12
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Learning Objectives12.1 Principles of Homeostasis
a) Define homeostasis
(b) Explain the basic principles of
homeostasis in terms of stimulus resulting
from a change in the internal environment, acorrective mechanism and a negative
feedback
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Homeostasis Homeostasis is
defined as the
maintenance of aconstant internal
environment.
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Changes in body temperature may result inenzyme inactivation or denaturation.
Any drastic changes in our blood and thesurrounding tissues fluid will affect chemicalreactions in the tissue cells and will harm thebody.
Cells must be bathed in tissue fluid of thecorrect pH and water potential. Enzyme
reaction will be affected.
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Negative Feedback Control The internal environment of our bodies
MUST have certain conditions within
tolerable limits to continue the healthyfunctioning.
Done by NEGATIVE FEEDBACK control.
Used to control blood sugar concentration,water concentration & temperature of the
blood.
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Negative Feedback A stimulus, which is the change in the internal
environment
A receptor that can detect the stimulus A self-regulatory corrective mechanism
A negative feedback to the receptor
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Stimulus
Condition
increases
Receptors
detects it Corrective
mechanism
Condition
decreases
Stimulus
Conditiondecreases
Receptor
detects it
Corrective
mechanism
Condition
rises
Normal
condition
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Organs involved in Homeostasis1. Skin (helps in temperature regulation)
2. Kidneys (helps in the water concentration of
the body)3. Brain (MASTERMIND)
4. Pancreas (produces insulin that helps in the
control of sugar concentration in the blood)
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Regulation of bloodglucose concentration Too much glucose in
blood
Stimulate pancreas to
secrete more insulin Causes the liver to
convert glucose to
glycogen
Blood glucose level drops
Achieved normal blood
glucose level
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Too little glucose in blood
Stimulate pancreas to secrete glucagon
which causes the liver to convert glycogento glucose
Blood glucose level rises
Achieved normal blood glucose level
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What Happens When GlucoseConcentration Rises?14 April 2012
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Stimulus
Blood glucose
concentration rises
above normal levels
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What Happens When Glucose Concentration Rises?
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Receptor
Islets of Langerhans
in pancreas stimulated
pancreas
Stimulus
Blood glucose
concentration rises
above normal levels
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What Happens When Glucose Concentration Rises?
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Receptor
Islets of Langerhans
in pancreas stimulated
Corrective Mechanism
Islets of Langerhans secretesmore insulin, which istransported by blood to liverand muscles
pancreas
liver
Stimulus
Blood glucose
concentration rises
above normal levels
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What Happens When Glucose Concentration Rises?
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Receptor
Islets of Langerhans
in pancreas stimulated
Permeability of cellsurface membraneto glucose increases
Corrective Mechanism
Islets of Langerhans secretesmore insulin, which istransported by blood to liverand muscles
pancreas
liver
Stimulus
Blood glucose
concentration rises
above normal levels
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What Happens When Glucose Concentration Rises?
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Receptor
Islets of Langerhans
in pancreas stimulated
Permeability of cellsurface membraneto glucose increases
Corrective Mechanism
Islets of Langerhans secretesmore insulin, which istransported by blood to liverand muscles
Liver and musclesconvert excessglucose to glycogen.Glycogen is stored inliver and muscles
pancreas
excess glucose glycogen
liver
Stimulus
Blood glucose
concentration rises
above normal levels
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What Happens When Glucose Concentration Rises?
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Receptor
Islets of Langerhans
in pancreas stimulated
Permeability of cellsurface membraneto glucose increases
Corrective Mechanism
Islets of Langerhans secretesmore insulin, which istransported by blood to liverand muscles
Liver and musclesconvert excessglucose to glycogen.Glycogen is stored inliver and muscles
Blood glucoseconcentrationdecreases andinsulin productionfalls
pancreas
excess glucose glycogen
liver
Stimulus
Blood glucose
concentration rises
above normal levels
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What Happens When Glucose Concentration Rises?
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Receptor
Islets of Langerhans
in pancreas stimulated
Permeability of cellsurface membraneto glucose increases
Corrective Mechanism
Islets of Langerhans secretesmore insulin, which istransported by blood to liverand muscles
Liver and musclesconvert excessglucose to glycogen.Glycogen is stored inliver and muscles
Blood glucoseconcentrationdecreases andinsulin productionfalls
pancreas
excess glucose glycogen
liver
Blood glucoseconcentrationreturns to normal
Stimulus
Blood glucose
concentration rises
above normal levels
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What Happens When Glucose Concentration Rises?
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Receptor
Islets of Langerhans
in pancreas stimulated
Stimulus
Blood glucose
concentration rises
above normal levels
Permeability of cellsurface membraneto glucose increases
Corrective Mechanism
Islets of Langerhans secretesmore insulin, which istransported by blood to liverand muscles
Liver and musclesconvert excessglucose to glycogen.Glycogen is stored inliver and muscles
Blood glucoseconcentrationdecreases andinsulin productionfalls
Negative feedback
Blood glucoseconcentrationreturns to normal
excess glucose glycogen
pancreas
liver
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What Happens When Glucose Concentration Rises?
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StimulusBlood glucose
concentration falls
below normal levels
What Happens When Glucose Concentration Falls?
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Receptor
Islets of Langerhans
in pancreas stimulated
StimulusBlood glucose
concentration falls
below normal levels
pancreas
What Happens When Glucose Concentration Falls?
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StimulusBlood glucose
concentration falls
below normal levels
pancreas
liver
Corrective Mechanism
Islets of Langerhans secretesmore glucagon, which istransported by blood to liverand muscles
Receptor
Islets of Langerhans
in pancreas stimulated
What Happens When Glucose Concentration Falls?
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Glucagon convertsstored glycogenback to glucose.From liver, glucoseenters bloodstream
StimulusBlood glucose
concentration falls
below normal levels
pancreas
liver
glycogen glucose
Corrective Mechanism
Islets of Langerhans secretesmore glucagon, which istransported by blood to liverand muscles
Receptor
Islets of Langerhans
in pancreas stimulated
What Happens When Glucose Concentration Falls?
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Glucagon convertsstored glycogenback to glucose.From liver, glucoseenters bloodstream
StimulusBlood glucose
concentration falls
below normal levels
pancreas
liver
glycogen glucoseReceptor
Islets of Langerhans
in pancreas stimulated
Corrective Mechanism
Islets of Langerhans secretesmore glucagon, which istransported by blood to liverand muscles
Blood glucoseconcentration risesand glucagonproduction decreases
What Happens When Glucose Concentration Falls?
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Glucagon convertsstored glycogenback to glucose.From liver, glucoseenters bloodstream
StimulusBlood glucose
concentration falls
below normal levels
pancreas
liver
glycogen glucoseReceptor
Islets of Langerhans
in pancreas stimulated
Corrective Mechanism
Islets of Langerhans secretesmore glucagon, which istransported by blood to liverand muscles
Blood glucoseconcentration risesand glucagonproduction decreases
Blood glucoseconcentrationreturns to normal
What Happens When Glucose Concentration Falls?
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liver
Receptor
Islets of Langerhans
in pancreas stimulated
Glucagon convertsstored glycogenback to glucose.From liver, glucoseenters bloodstream
Corrective Mechanism
Islets of Langerhans secretesmore glucagon, which istransported by blood to liverand muscles
Negative feedback
StimulusBlood glucose
concentration falls
below normal levels
Blood glucoseconcentrationreturns to normal
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What Happens When Glucose Concentration Falls?
Blood glucoseconcentration risesand glucagonproduction decreases
glycogen glucose
pancreas
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Water potentialof blooddecreases
Stimulatepituitary glandto secrete moreADH More waterreabsorbed bykidney tubules,less water isexcreted Urine is moreconcentrated,
less urineproduced Return to normalcondition
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Water potential of blood increases Stimulate pituitary gland tosecrete less ADH Less water reabsorbed by kidneytubules, more water is excreted Urine is more diluted, more urine
produced Return to normal condition
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Learning Objectives
12.2 Structure and function of the skin
(c) Identify on a diagram of the skin: hairs, sweat
glands, temperature receptors, blood vessels and
fatty tissue
(d) Describe the maintenance of a constant body
temperature in humans in terms of insulation and the
role of: temperature receptors in the skin, sweating,shivering, blood vessels near the skin surface and the
co-ordinating role of the brain
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Skin
Largest organ of the human body.
An important sense organ
Barrier between the body and the externalenvironment
Organ that regulates our body temperature.
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Skin
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Epidermis
outer layer of the skin :-a. Cornified layer (dead cells)
Protects the body from water loss, invasion ofmicrobes & mechanical, thermal & chemicaldamage.
b. Granular layer
New cells undergo cell division
c. Malpighian layer
to replace dead cells from the cornified layer
pigmented cells (melanin) protects our skin against
harmful UV light of the sun
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Functions of the Epidermis
1. Layer is water-resistant (waterproof)
2. Prevents evaporation
of water from skin3. Prevents germs from
entrying into the body.
4. Protective layer,preventing mechnicalinjury.
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Dermis
Consists mainly of fibrous tissue and many otherstructures:-
(a) Blood vessels
numerous blood vessels
Arterioles that carry blood are controlled byvasometer nerves.
Nerves bring about contraction & dilation of thearteries.
Arterioles dilate (vasodilation) --> more blood issent to the skin.
Arterioles contract (vasoconstriction) --> less blood
is sent to the skin.
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Dermis
(b) Hair
Common feature of mammals.
Grow inside the hair follicle
At the base of the follicle is a mass of tissue
containing blood capillaries.
Attached to the hair follicles are the hairerector muscles. (contract --> causes the hair
to stand)
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Dermis
(c ) Sweat glands
sweat is secreted in the sweat glands.
Sweat glands ---> sweat duct ---> sweat pore
surface of skin.
Sweat = urea + water + salt (sodium chloride)
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Dermis
(d) Temperature receptors
nerve endings are found in the epidermis and
dermis. Form sense organs
Enable us to sense pain, pressureand
temperature changes in the externalenvironment.
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NERVE
ENDINGS
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Dermis
(e) Fatty Tissue
--> Fat cells are present where fat is stored.
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Dermis
(f) Sebaceous glands
2 glands open into each hair follicle.
Secreting an oily substance (sebum) into hairfollicle.
Sebum lubricates the hair and keeps the skin
soft and smooth. Prevents dehydration of the skin.
Has an antiseptic action.
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Control of body
temperature
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Skin
Able to detect temperature change in the
external environment.
A change in atmospheric temperature -->detected by temperature receptors on the skin
--> start some mechanisms to control the
temperature.
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The Brain
Hypothalamus is the control centre for
temperature.
Detects temperature changes in the blood.
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What happens when temperature rises?
Hypothalamus triggers off the following:-
1. Decreased metabolic rate of the cells, resulting inless heat being produced.
2. Relaxation of skeletal muscles to reduce heatproduction. Causes the hair to lie flat
3. Vasodilation causing arterioles to increase bloodsupply to the skin . More heat can be lost through
the skin.
4. More sweat is produced. As sweat is removedmore latent heat is removed.
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What happens when temperature falls?
(a) Increased metabolic rate, resulting in moreheat being produced.
(b) Shivering due to the contraction of skeletalmuscles. (increases heat production)
(c) Causes hair to stand.
(d) Vasoconstriction causing arterioles in the
skin to constrict.
(e) Blood is diverted from the skin to reduceheat loss.
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Body Temp37 C
Detected by
hypothalamusRise in Blood
Temperature
Heat released
During exerciseHeat loss
Body Temp37 C
Increased sweating
Vasodilation
Cold
environment
Drop in blood
temperature
Blood temp
rises
Decreased sweating
Vasoconstriction
shiveringDetected by
hypothalamus
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Regulating Body Temperature - on a Hot Day
14 April 2012
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Regulating Body Temperature on a Hot Day
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Regulating Body Temperature on a Hot Day
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
blood capillaries
hair folliclehair
arteriole
erector muscle
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
Regulating Body Temperature on a Hot Day
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
arteriole
capillariesskin surface
Arterioles in
skin dilate
1
More blood flows to
capillaries in skin
2
3
Greater heat loss
4
Shunt vessels constrict
Regulating Body Temperature on a Hot Day
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
sweat duct
sweat pore
sweat gland
Sweat glands
more active
Sweat
production
increases
More latent heat lost as sweat evaporates
6
7
5
Regulating Body Temperature on a Hot Day
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Hair erector
muscles in
skin relax
erector muscle
blood capillaries
hair folliclehair
arteriole
8
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
Regulating Body Temperature on a Hot Day
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
Corrective Mechanism
Increase in heat loss anddecrease in heat
production
Regulating Body Temperature on a Hot Day
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
Corrective Mechanism
Increase in heat loss anddecrease in heat
production
Decreased
metabolic rate
reduces heatproduction
egu at g ody e pe atu e o a ot ay
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
Corrective Mechanism
Increase in heat loss anddecrease in heat
production
Blood temperature
returns to normal levels
Decreased
metabolic rate
reduces heatproduction
g g y p y
Regulating Body Temperature - on a Hot Day
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Stimulus
Blood and skintemperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
Corrective Mechanism
Increase in heat loss anddecrease in heat
production
Blood temperature
returns to normal levels
Negative
feedback
Decreased
metabolic rate
reduces heatproduction
g g y p y
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Regulating Body Temperature - on a Cold Day
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Regulating Body Temperature - on a Cold Day
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Stimulus
Blood and skin
temperatures fall
g g y p y
Regulating Body Temperature - on a Cold Day
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Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
g g y p y
Regulating Body Temperature - on a Cold Day
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blood capillariesarteriole
hair hair follicle
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
erector muscles
g g y p y
Regulating Body Temperature - on a Cold Day
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Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Less blood flows to
capillaries in skin
Arterioles in
skin constrictShunt vessels dilate
skin surfacecapillaries
arteriole
1
2
3
Less heat loss
4
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
g g y p y
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Sweat glands
less active
Sweat
production
decreases
Less latent heat lost
sweat pore
sweat duct
sweat gland
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
56
7
g g y p y
Regulating Body Temperature - on a Cold Day
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Hair erector
muscles in
skin contract
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erector muscles
blood capillariesarteriole
hair hair follicle
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
8
Regulating Body Temperature - on a Cold Day
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Shivering occurs when
insufficient heat is produced
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Hypothalamus of brain
is
stimulated and sends
nerve impulses to
relevant body parts
Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Regulating Body Temperature - on a Cold Day
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Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Increased
metabolic rate
increases heatproduction
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
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Blood temperature
returns to normal levels
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Increased
metabolic rate
increases heatproduction
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
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Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Increased
metabolic rate
increases heatproduction
Blood temperature
returns to normal levels
Negative
feedback
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Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
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Chapter 12 HomeostasisHomeostasis (Concept Map)14 April 2012
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HOMEOSTASIS
The maintenance of a constant internal environment
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Principles of Homeostasis
HOMEOSTASIS
The maintenance of a constant internal environment
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Principles of Homeostasis
Stimulus
Change ininternalenvironment
HOMEOSTASIS
The maintenance of a constant internal environment
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Principles of Homeostasis
Stimulus
Change ininternalenvironment
HOMEOSTASIS
The maintenance of a constant internal environment
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Receptors
Detect thechange
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Principles of Homeostasis
Stimulus
Change ininternalenvironment
HOMEOSTASIS
The maintenance of a constant internal environment
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Receptors
Detect thechange
Self-corrective Mechanism
To rectify thechange
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Principles of Homeostasis
Stimulus
Change ininternalenvironment
HOMEOSTASIS
The maintenance of a constant internal environment
14 April 2012Copyright 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 82
Receptors
Detect thechange
Self-corrective Mechanism
To rectify thechange
Examples
Regulation ofblood glucoseconcentration
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Principles of Homeostasis
Stimulus
Change ininternalenvironment
HOMEOSTASIS
The maintenance of a constant internal environment
14 April 2012Copyright 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 83
Receptors
Detect thechange
Self-corrective Mechanism
To rectify thechange
Examples
Regulation ofblood glucoseconcentration
Regulation ofblood waterpotential
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Principles of Homeostasis
Stimulus
Change ininternalenvironment
HOMEOSTASIS
The maintenance of a constant internal environment
14 April 2012Copyright 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 84
Receptors
Detect thechange
Self-corrective Mechanism
To rectify thechange
Examples
Regulation ofblood glucoseconcentration
Regulation ofblood waterpotential
Regulation ofbody temperature
HOMEOSTASIS
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Principles of Homeostasis
Stimulus Receptors Self-corrective Mechanism Negative Feedback
Change ininternalenvironment
Detect thechange
Regulation ofblood glucoseconcentration
Examples
To rectify thechange
Regulation ofblood waterpotential
Regulation ofbody temperature
The reverseeffect of thechange
HOMEOSTASIS
The maintenance of a constant internal environment