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

1. HOMEOSTASIS
BY
SAI DATRI ARIGE
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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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7. SWEATING
The
skin
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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

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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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16. DYNAMIC EQUILIBRIUM
 Homeostasis is also called dynamic equilibrium:
 Conditions do fluctuate, but within an acceptable range
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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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20. EXAMPLE: BLOOD PRESSURE
REGULATION
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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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