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Homeostasis
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A day at the sauna
How does the body react to change?
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Saving energy?
Sayid has decided to save energy by staying in bed all day.
How much of his energy do you think this will save?
Surprisingly, the answer is only about 30%. The other 70%
keeps his body temperature at 37°C, and the fluid
surrounding around his cells at just the right concentration.
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What is homeostasis?
The body uses so much energy, even during sleep, because
it must maintain a constant internal environment.
This process of keeping things the
same is called homeostasis.
Nervous and hormonal control
systems ensure that the body
maintains a constant temperature.
These control systems also make
sure that the body has steady levels
of water, ions and blood sugar.
Homeostasis allows the body’s cells and enzymes to work at
their optimum level.
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Maintaining internal conditions
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Control systems
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The organs of homeostasis
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Why control temperature?
Environmental temperature is
constantly changing. One minute it can
be very hot, the next very cold.
Even slight changes in body temperature can have a life-
threatening effect on health. If body temperature falls too low,
reactions become too slow for cells to survive: too high, and
the body’s enzymes are at risk of denaturing.
Despite this, the body must be kept at
a constant temperature of 37°C.
Why?
This is the optimum temperature for the
body’s enzymes.
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What is core body temperature?
The vital organs located deep within the body, such as the
heart, liver and kidneys, are maintained at 37°C. This is
the core body temperature.
Skin temperature at the body's
extremities, such as the fingers
and toes, is usually lower than
the core body temperature.
This reduces the energy lost.
On a warm day, skin temperature may be just 1°C lower than
the core body temperature, but on a very cold day it could be
up to 9°C lower.
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Measuring body temperature
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Finding the right balance
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Too hot…or too cold?
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How is temperature controlled?
Body temperature is monitored and controlled by temperature
receptors in the skin and brain.hypothalamus
These receptors detect changes
in the temperature of blood
flowing through those areas.
The thermoregulatory centre in the
brain is called the hypothalamus.
If body temperature deviates from 37°C, the hypothalamus
and skin receptors send out electrical signals that trigger
actions or behaviours that increase or decrease heat loss.
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Maintaining the core temperature
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Why do we shiver?
When core body temperature drops, muscles begin to twitch.
This rapid contraction and relaxation of the muscles is
called shivering.
Shivering generates heat, which raises body
temperature.
Goosebumps involuntarily appear when a
person becomes cold. Goosebumps are
caused by the tiny muscles at the base of
body hairs pulling the hairs erect.
The upright hairs trap an insulating layer
of air, which helps reduce heat loss.
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The structure of the skin
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Vasoconstriction and warming up
Why do people go pale when they are cold?
Vasoconstriction is
caused by contraction
of the muscular wall of
the blood vessels.
When core body temperature falls, blood vessels in the skin
get narrower. This is called vasoconstriction.
This reduces the volume
of blood flowing near the
skin surface, and
reduces the amount of
heat lost from the body.
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Vasodilation and cooling down
Why do people turn red when they are hot?
Additional cooling occurs with
the production of sweat from
sweat glands.
Vasodilation allows a larger volume of blood to flow near the
skin surface, transferring heat to the environment. This cools
the body down.
When core body temperature rises, blood vessels in the skin
get wider. This is called vasodilation.
As the sweat evaporates it
transfers heat away from the body.
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Responding to change
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Negative feedback in the body
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Thermoregulation: true or false?
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Glossary
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Multiple-choice quiz
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