Thermoregulation
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Transcript Thermoregulation
Thermoregulation
Chapter 8
Homeostasis of body temperature and
body fluids
© 2010 McGraw-Hill Australia
Humans
In humans, body temperature is relatively constant
The usual body temperature is 36.8C
In the body, heat gained = heat lost
This process is called thermoregulation, a term
used to describe the processes which maintain the
balance between heat production and heat loss
© 2010 McGraw-Hill Australia
© 2010 McGraw-Hill Australia
Why Thermoregulate?
Chemical reactions occurring in cells are very
heat-sensitive
Enzymes that control cellular activity are heatsensitive
© 2010 McGraw-Hill Australia
Rising Body Temperature
Rising body temperature prompts heat
loss in the body through:
blood flow to the skin
metabolic rate
behavioural responses
sweating
© 2010 McGraw-Hill Australia
Blood Flow to Skin
Vasodilation:
in response to rising temperature, the body
increases blood flow to the skin
is controlled by the autonomic nervous system
results in an increase in blood flow to the skin,
allowing heat loss via radiation, conduction,
convection and evaporation
prompts cooling of the blood that is flowing
through the skin
© 2010 McGraw-Hill Australia
Metabolic Rate
The metabolic rate changes through a reduction
in the secretion of thyroxine
This results in a decrease in metabolic rate
The decrease in metabolic rate causes less heat to
be produced in the body
© 2010 McGraw-Hill Australia
Behavioural Responses
We change our behavioural responses by:
staying still (decreasing activity)
staying in the shade
air conditioning
wearing less clothing
© 2010 McGraw-Hill Australia
Sweat
Sweat is controlled by the sympathetic nervous
system
It is secreted from sweat glands to skin
Sweat contains sodium chloride, urea, lactic acid
and potassium ions
Sweat cools by evaporating from the body
Sweat doesn’t work in a humid environment
Environmental temperature > body temp for
sweating to be effective
© 2010 McGraw-Hill Australia
Rising Body Temperature
© 2010 McGraw-Hill Australia
Falling Body Temperature
Falling body temperature prompts:
changes in blood flow to the skin
changes in metabolic rate
shivering
behavioural responses
© 2010 McGraw-Hill Australia
Blood Flow to Skin
In response to falling temperatures, the body
restricts blood flow to the skin. This process is
called vasoconstriction
Vasoconstriction:
is controlled by the sympathetic nervous system
decreases blood flow to the skin from internal organs,
which
• decreases the transfer of heat from the internal body organs
to the skin
• allows less heat to be lost from the body surface
• cools the skin
© 2010 McGraw-Hill Australia
Falling Body Temperature – Skin
© 2010 McGraw-Hill Australia
The Hypothalamus and the
Adrenal Medulla
The hypothalamus stimulates the adrenal medulla
via sympathetic nerves
The medulla secretes adrenaline and
noradrenaline into the blood
This increases cellular metabolism, increasing
heat production
This process helps maintain internal body
temperature
© 2010 McGraw-Hill Australia
The Hypothalamus and the
Anterior Pituitary
The hypothalamus also stimulates the anterior
lobe of the pituitary
The anterior pituitary secretes thyroid stimulating
hormone (TSH)
TSH acts on the thyroid gland
The thyroid gland releases thyroxine into the
blood
This increases metabolic rate, increasing body
temperature
© 2010 McGraw-Hill Australia
Shivering
Shivering is actually rhythmic muscle tremors
occurring at a rate of around ten to twenty per
second
The hypothalamus stimulates parts of the brain
that increase skeletal muscle tone
This increases body heat production
© 2010 McGraw-Hill Australia
Behavioural Responses
We change our behavioural responses by:
huddling
curling into a ball
putting on more clothes
using a heating device
© 2010 McGraw-Hill Australia
© 2010 McGraw-Hill Australia
Complete this negative feedback loop for rising body
temperature.
© 2010 McGraw-Hill Australia
Complete this negative feedback loop for falling body
temperature.
© 2010 McGraw-Hill Australia