The maintenance of a constant environment in the body is called Homeostasis
Homeostasis is also called dynamic equilibrium
equilibrium maintained BY:
Feedback systems
Negative feedback
Positive feedback
Negative feedback: Response triggered by changed conditions serves to reverse the change
E.g., Body temperature increases
Skin blood vessels dilate
Body temperature decreases
Positive feedback: The response triggered by changing conditions serves to move the variable even further away from its steady state
E.g., uterine contractions are stimulated by oxytocin
baby moves towards cervix
more oxytocin is released
2. IMPORTANT VARIABLES WITHIN
THE BODY:
blood sugar
fluid balance
body temperature
oxygen levels
blood pressure
pH
These variables must stay within certain ranges.
Changes in the external environment can cause these
variables to change.
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3. WHAT IS HOMEOSTASIS?
Body cells work best if they have the correct
Temperature
Water levels
Glucose concentration
Your body has mechanisms to keep the cells in a
constant environment.
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4. WHAT IS HOMEOSTASIS?
The maintenance of a
constant environment in
the body is called
Homeostasis
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5. CONTROLLING BODY TEMPERATURE
All mammals maintain a constant body
temperature.
Human beings have a body temperature
of about 37ºC.
E.g. If your body is in a hot environment your
body temperature is 37ºC
If your body is in a cold environment your body
temperature is still 37ºC
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6. WHAT MECHANISMS ARE
THERE TO COOL THE BODY
DOWN?
1. Sweating
When your body is hot, sweat glands are
stimulated to release sweat.
The liquid sweat turns into a gas (it evaporates)
To do this, it needs heat.
It gets that heat from your skin.
As your skin loses heat, it cools down.
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8. What mechanisms are there toWhat mechanisms are there to coolcool
the body down?the body down?
2. Vasodilation
Your blood carries most of the heat energy
around your body.
There are capillaries underneath your skin that
can be filled with blood if you get too hot.
This brings the blood closer to the surface of
the skin so more heat can be lost.
This is why you look red when you are hot! 8
9. If the temperature
rises, the blood
vessel dilates (gets
bigger).
This means more heat is lost from the surface of the skin
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10. WHAT MECHANISMS ARE THERE TO
WARM THE BODY UP?
1. Vasoconstriction
This is the opposite of vasodilation
The capillaries underneath your skin get
constricted (shut off).
This takes the blood away from the surface of
the skin so less heat can be lost.
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11. If the temperature
falls, the blood
vessel constricts
(gets shut off).
This means less heat is lost from the surface of the skin
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12. WHAT MECHANISMS ARE THERE TO
WARM THE BODY UP?
2. Piloerection
This is when the hairs on your skin “stand up”
.
It is sometimes called “goose bumps” or
“chicken skin”!
The hairs trap a layer of air next to the skin
which is then warmed by the body heat
The air becomes an insulating layer. 12
14. COMPONENTS OF A HOMEOSTATIC
CONTROL SYSTEM:
Component Function
Monitor detects a change in variable
Co-ordinating centre receives a message from the monitor. directs
a response via a regulator.
Regulator carries out the response initiated by the co-
ordinating centre
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15. THE HYPOTHALAMUS
Part of the brain
Often serves as the co-ordinating centre:
Receives messages from monitors
Initiates a hormonal/nervous response
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17. How is dynamic equilibrium maintained?
Feedback systems
Negative feedback
Positive feedback
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18. NEGATIVE FEEDBACK
Negative feedback: Response triggered by
changed conditions serves to reverse the change
E.g., Body temperature increases Skin blood vessels
dilate Body temperature decreases
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21. POSITIVE FEEDBACK
Positive feedback: The response triggered by
changing conditions serves to move the variable
even further away from its steady state
E.g., uterine contractions are stimulated by
oxytocin baby moves towards cervix more
oxytocin is released
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