Homeostasis
Chapter 12
Learning Objectives
12.1 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, a
corrective mechanism and a negative
feedback
Homeostasis

Homeostasis is
defined as the
maintenance of a
constant internal
environment.



Changes in body temperature may result in
enzyme inactivation or denaturation.
Any drastic changes in our blood and the
surrounding tissues fluid will affect chemical
reactions in the tissue cells and will harm the
body.
Cells must be bathed in tissue fluid of the
correct pH and water potential. Enzyme
reaction will be affected.
Negative Feedback Control



The internal environment of our bodies
MUST have certain conditions within
tolerable limits to continue the healthy
functioning.
Done by NEGATIVE FEEDBACK control.
Used to control blood sugar concentration,
water concentration & temperature of the
blood.
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
Receptors
detects it
Stimulus
Condition
increases
Normal
condition
Corrective
mechanism
Condition
decreases
Condition
rises
Stimulus
Condition
decreases
Receptor
detects it
Corrective
mechanism
Organs involved in Homeostasis
1.
2.
3.
4.
Skin (helps in temperature regulation)
Kidneys (helps in the water concentration of
the body)
Brain (MASTERMIND)
Pancreas (produces insulin that helps in the
control of sugar concentration in the blood)

Regulation of blood
glucose 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




Too little glucose in blood
Stimulate pancreas to secrete glucagon
which causes the liver to convert glycogen
to glucose
Blood glucose level rises
Achieved normal blood glucose level
What Happens When Glucose
Concentration Rises?
18 April 2021
What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
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18 April 2021
12
What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
pancreas
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18 April 2021
13
What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more insulin, which is
transported by blood to liver
and muscles
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18 April 2021
14
What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more insulin, which is
transported by blood to liver
and muscles
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Permeability of cell
surface membrane
to glucose increases
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What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
excess glucose  glycogen
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more insulin, which is
transported by blood to liver
and muscles
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Liver and muscles
convert excess
glucose to glycogen.
Glycogen is stored in
liver and muscles
Permeability of cell
surface membrane
to glucose increases
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What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
Blood glucose
concentration
decreases and
insulin production
falls
excess glucose  glycogen
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more insulin, which is
transported by blood to liver
and muscles
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Liver and muscles
convert excess
glucose to glycogen.
Glycogen is stored in
liver and muscles
Permeability of cell
surface membrane
to glucose increases
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What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
Blood glucose
concentration
returns to normal
excess glucose  glycogen
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more insulin, which is
transported by blood to liver
and muscles
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Blood glucose
concentration
decreases and
insulin production
falls
Liver and muscles
convert excess
glucose to glycogen.
Glycogen is stored in
liver and muscles
Permeability of cell
surface membrane
to glucose increases
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What Happens When Glucose Concentration Rises?
Stimulus
Blood glucose
concentration rises
above normal levels
Blood glucose
concentration
returns to normal
Blood glucose
concentration
decreases and
insulin production
falls
Negative feedback
Receptor
Islets of Langerhans
in pancreas stimulated
excess glucose  glycogen
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more insulin, which is
transported by blood to liver
and muscles
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Liver and muscles
convert excess
glucose to glycogen.
Glycogen is stored in
liver and muscles
Permeability of cell
surface membrane
to glucose increases
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19
What Happens When Glucose Concentration Falls?
Stimulus
Blood glucose
concentration falls
below normal levels
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18 April 2021
20
What Happens When Glucose Concentration Falls?
Stimulus
Blood glucose
concentration falls
below normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
pancreas
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18 April 2021
21
What Happens When Glucose Concentration Falls?
Stimulus
Blood glucose
concentration falls
below normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more glucagon, which is
transported by blood to liver
and muscles
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18 April 2021
22
What Happens When Glucose Concentration Falls?
Stimulus
Blood glucose
concentration falls
below normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
glycogen  glucose
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more glucagon, which is
transported by blood to liver
and muscles
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Glucagon converts
stored glycogen
back to glucose.
From liver, glucose
enters bloodstream
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23
What Happens When Glucose Concentration Falls?
Stimulus
Blood glucose
concentration falls
below normal levels
Receptor
Islets of Langerhans
in pancreas stimulated
Blood glucose
concentration rises
and glucagon
production decreases
glycogen  glucose
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more glucagon, which is
transported by blood to liver
and muscles
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Glucagon converts
stored glycogen
back to glucose.
From liver, glucose
enters bloodstream
18 April 2021
24
What Happens When Glucose Concentration Falls?
Stimulus
Blood glucose
concentration falls
below normal levels
Blood glucose
concentration
returns to normal
Receptor
Islets of Langerhans
in pancreas stimulated
glycogen  glucose
Blood glucose
concentration rises
and glucagon
production decreases
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more glucagon, which is
transported by blood to liver
and muscles
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Glucagon converts
stored glycogen
back to glucose.
From liver, glucose
enters bloodstream
18 April 2021
25
What Happens When Glucose Concentration Falls?
Stimulus
Blood glucose
concentration falls
below normal levels
Blood glucose
concentration
returns to normal
Blood glucose
concentration rises
and glucagon
production decreases
Negative feedback
Receptor
Islets of Langerhans
in pancreas stimulated
glycogen  glucose
liver
pancreas
Corrective Mechanism
Islets of Langerhans secretes
more glucagon, which is
transported by blood to liver
and muscles
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Glucagon converts
stored glycogen
back to glucose.
From liver, glucose
enters bloodstream
18 April 2021
26





Water potential
of blood
decreases
Stimulate
pituitary gland
to secrete more
ADH
More water
reabsorbed by
kidney tubules,
less water is
excreted
Urine is more
concentrated,
less urine
produced
Return to normal
condition





Water potential of blood increases
Stimulate pituitary gland to
secrete less ADH
Less water reabsorbed by kidney
tubules, more water is excreted
Urine is more diluted, more urine
produced
Return to normal condition
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
Skin




Largest organ of the human body.
An important sense organ
Barrier between the body and the external
environment
Organ that regulates our body temperature.
Skin
Epidermis
outer layer of the skin :a. Cornified layer (dead cells)
 Protects the body from water loss, invasion of
microbes & mechanical, thermal & chemical
damage.
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
Functions of the Epidermis
1.
2.
3.
4.
Layer is waterresistant (waterproof)
Prevents evaporation
of water from skin
Prevents germs from
entrying into the body.
Protective layer,
preventing mechnical
injury.
Dermis

(a)





Consists mainly of fibrous tissue and many other
structures:Blood vessels
numerous blood vessels
Arterioles that carry blood are controlled by
vasometer nerves.
Nerves bring about contraction & dilation of the
arteries.
Arterioles dilate (vasodilation) --> more blood is
sent to the skin.
Arterioles contract (vasoconstriction) --> less blood
is sent to the skin.
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 “hair
erector” muscles. (contract --> causes the hair
to stand)
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)
Dermis
(d) Temperature receptors
 nerve endings are found in the epidermis and
dermis.
 Form sense organs
 Enable us to sense pain, pressure and
temperature changes in the external
environment.
NERVE
ENDINGS
Dermis
(e) Fatty Tissue
--> Fat cells are present where fat is stored.
Dermis
(f) Sebaceous glands
 2 glands open into each hair follicle.
 Secreting an oily substance (sebum) into hair
follicle.
 Sebum lubricates the hair and keeps the skin
soft and smooth.
 Prevents dehydration of the skin.
 Has an antiseptic action.
Control of body
temperature
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.
The Brain


Hypothalamus is the control centre for
temperature.
Detects temperature changes in the blood.
What happens when temperature rises?
Hypothalamus triggers off the following:1.
Decreased metabolic rate of the cells, resulting in
less heat being produced.
2.
Relaxation of skeletal muscles to reduce heat
production. Causes the hair to lie flat
3.
Vasodilation causing arterioles to increase blood
supply to the skin . More heat can be lost through
the skin.
4.
More sweat is produced. As sweat is removed
more latent heat is removed.
What happens when temperature falls?
(a)
(b)
(c)
(d)
(e)
Increased metabolic rate, resulting in more
heat being produced.
Shivering due to the contraction of skeletal
muscles. (increases heat production)
Causes hair to stand.
Vasoconstriction causing arterioles in the
skin to constrict.
Blood is diverted from the skin to reduce
heat loss.
Rise in Blood
Temperature
Detected by
hypothalamus
Heat released
During exercise
Heat loss
Body Temp
37 C
Body Temp
37 C
Cold
environment
Drop in blood
temperature
Increased sweating
Vasodilation
Blood temp
rises
Detected by
hypothalamus
Decreased sweating
Vasoconstriction
shivering
Regulating Body Temperature - on a Hot Day
18 April 2021
Regulating Body Temperature - on a Hot Day
Stimulus
Blood and skin
temperatures rise
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55
Regulating Body Temperature - on a Hot Day
Stimulus
Blood and skin
temperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
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18 April 2021
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Regulating Body Temperature - on a Hot Day
hair
hair follicle
arteriole
blood capillaries
Stimulus
Blood and skin
temperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
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erector muscle
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
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Regulating Body Temperature - on a Hot Day
4
Greater heat loss
Stimulus
Blood and skin
temperatures rise
skin surface
capillaries
1
Arterioles in
skin dilate
3
Shunt vessels constrict
arteriole
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
2
More blood flows to
capillaries in skin
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Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
58
Regulating Body Temperature - on a Hot Day
7
More latent heat lost as sweat evaporates
sweat pore
Stimulus
Blood and skin
temperatures rise
sweat duct
6
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
Sweat
production
increases
sweat gland
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5
Sweat glands
more active
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
59
Regulating Body Temperature - on a Hot Day
hair
hair follicle
arteriole
blood capillaries
8
Stimulus
Blood and skin
temperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
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Hair erector
muscles in
skin relax
erector muscle
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
60
Regulating Body Temperature - on a Hot Day
Stimulus
Blood and skin
temperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
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Corrective Mechanism
Increase in heat loss and
decrease in heat
production
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
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Regulating Body Temperature - on a Hot Day
Decreased
metabolic rate
reduces heat
production
Stimulus
Blood and skin
temperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
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Corrective Mechanism
Increase in heat loss and
decrease in heat
production
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
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62
Regulating Body Temperature - on a Hot Day
Blood temperature
returns to normal levels
Stimulus
Blood and skin
temperatures rise
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
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Decreased
metabolic rate
reduces heat
production
Corrective Mechanism
Increase in heat loss and
decrease in heat
production
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
63
Regulating Body Temperature - on a Hot Day
Blood temperature
returns to normal levels
Stimulus
Blood and skin
temperatures rise
Decreased
metabolic rate
reduces heat
production
Corrective Mechanism
Increase in heat loss and
decrease in heat
production
Negative
feedback
Receptor
Temperature receptors
detect changes and send
nerve impulses to the brain
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Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
64
Regulating Body Temperature - on a Cold Day
18 April 2021
Regulating Body Temperature - on a Cold Day
Stimulus
Blood and skin
temperatures fall
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18 April 2021
66
Regulating Body Temperature - on a Cold Day
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
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18 April 2021
67
Regulating Body Temperature - on a Cold Day
hair hair follicle
blood capillaries
arteriole
Stimulus
Blood and skin
temperatures fall
erector muscles
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
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Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
68
Regulating Body Temperature - on a Cold Day
4
Less heat loss
Stimulus
Blood and skin
temperatures fall
skin surface
capillaries
1
3
Arterioles in
skin constrict
Shunt vessels dilate
arteriole
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
2
Less blood flows to
capillaries in skin
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Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
69
Regulating Body Temperature - on a Cold Day
7
Stimulus
Blood and skin
temperatures fall
Less latent heat lost
sweat pore
sweat duct
6
Sweat
production
decreases
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
sweat gland
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5
Sweat glands
less active
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
70
Regulating Body Temperature - on a Cold Day
hair hair follicle
blood capillaries
arteriole
Stimulus
Blood and skin
temperatures fall
8
Hair erector
muscles in
skin contract
erector muscles
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
71
Regulating Body Temperature - on a Cold Day
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
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Hypothalamus of brain
is
stimulated and sends
nerve impulses to
relevant body
parts 72
18 April 2021
Regulating Body Temperature - on a Cold Day
Increased
metabolic rate
increases heat
production
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
73
Regulating Body Temperature - on a Cold Day
Blood temperature
returns to normal levels
Stimulus
Blood and skin
temperatures fall
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Increased
metabolic rate
increases heat
production
Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
74
Regulating Body Temperature - on a Cold Day
Blood temperature
returns to normal levels
Stimulus
Blood and skin
temperatures fall
Negative
feedback
Receptor
Temperature receptors
detect changes and send
nerve impulses to the
brain
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Increased
metabolic rate
increases heat
production
Corrective Mechanism
Decrease in heat loss
and increase in heat
production
Hypothalamus of brain
is stimulated and sends
nerve impulses to
relevant body parts
18 April 2021
75
Chapter 12 Homeostasis
Homeostasis (Concept Map)
18 April 2021
HOMEOSTASIS
The maintenance of a constant internal environment
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77
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
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78
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Change in
internal
environment
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18 April 2021
79
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Receptors
Change in
internal
environment
Detect the
change
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80
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Receptors
Self-corrective Mechanism
Change in
internal
environment
Detect the
change
To rectify the
change
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18 April 2021
81
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Receptors
Self-corrective Mechanism
Change in
internal
environment
Detect the
change
To rectify the
change
Examples
Regulation of
blood glucose
concentration
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18 April 2021
82
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Receptors
Self-corrective Mechanism
Change in
internal
environment
Detect the
change
To rectify the
change
Examples
Regulation of
blood glucose
concentration
Regulation of
blood water
potential
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
18 April 2021
83
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Receptors
Self-corrective Mechanism
Change in
internal
environment
Detect the
change
To rectify the
change
Examples
Regulation of
blood glucose
concentration
Regulation of
blood water
potential
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Regulation of
body temperature
18 April 2021
84
HOMEOSTASIS
The maintenance of a constant internal environment
Principles of Homeostasis
Stimulus
Receptors
Self-corrective Mechanism
Change in
internal
environment
Detect the
change
To rectify the
change
Negative Feedback
The reverse
effect of the
change
Examples
Regulation of
blood glucose
concentration
Regulation of
blood water
potential
Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd.
Regulation of
body temperature
18 April 2021
85