Detecting Temperature Change

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Detecting Temperature Change
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External temperature change

• Skin is the barrier between our body and the
  external environment and can be 2 or 3 degrees
  below core body temp
• Core body temp is maintained at about 37 degrees
  C
• Changes in the external temp causes changes in
  the temp of exposed skin. These changes are
  detected by two kinds of temp receptors
• - one detects cooling
• - one detects warming

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External temperature change

• If there is a reduction in skin temp, the cold
  receptors register the change by increasing the
  rate of discharge of electrical information along
  the affector neurons

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External temperature change

• If there is an increase in skin temperature, the
  heat receptors increase their rate of discharge
  along the affector neurons

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External temperature change

• The number of different kinds of temperature
  receptors vary in different parts of the skin

Affector or sensory neurons transmit impulses
from skin temperature receptors to the
Hypothalamus in the brain
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Hypothalamus
The temperature control centre of the body
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Mechanism of Thermoregulation
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Hypothalamus

• The hypothalamus plays a most significant role
  in the maintenance of core body temperature.
• It receives information about temperature change
  via sensory nerves from various parts of the body
  as well as detecting temperature change itself.
• The messages sent out by the hypothalamus in
  response depend on whether the information is
  that the temperature is higher or lower than 37C

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Draw a negative feedback loop for temperature
change
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Internal temperature change

• Changes in core body temp are detected by a
  number of temp receptors within the body

The most important of these are large numbers of
temperature-sensitive receptors in the
hypothalamus of the brain. The majority of
these, ¾ of the total, are sensitive to heat, the
remaining sensitive to cold.
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Internal temperature change

• Other deep body temp receptors are near the
  spinal cord, around large veins and in parts of
  the digestive system.
• These transmit impulses via affector neurons to
  the hypothalamus.

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Maintaining Core Temperature
Ways of gaining heat Ways of losing heat
Basic metabolic processes Evaporation of sweat
Shivering Panting
Exercise or other muscular activity Convection
Radiation and conduction to the body Radiation and conduction from the body
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HEAT TRANSFER PRINCIPLES

• CONDUCTION is the transfer of energy through
  matter from particle to particle.
• CONVECTION is the transfer of heat by the actual
  movement of the warmed matter.
• RADIATION Electromagnetic waves that directly
  transport ENERGY through space.

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CONDUCTION

• Conduction is the transfer of energy through
  matter from particle to particle. It is the
  transfer and distribution of heat energy from
  atom to atom within a substance.
• For example, a spoon in a cup of hot soup
  becomes warmer because the heat from the soup is
  conducted along the spoon.
• Conduction is most effective in solids-but it
  can happen in fluids.
• Fun fact Have you ever noticed that metals
  tend to feel cold? Believe it or not, they are
  not colder! They only feel colder because they
  conduct heat away from your hand. You perceive
  the heat that is leaving your hand as cold.

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CONVECTION

• Convection is the transfer of heat by the actual
  movement of the warmed matter.
• Heat leaves the coffee cup as the currents of
  steam and air rise.
• Convection is the transfer of heat energy in a
  gas or liquid by movement of currents. (It can
  also happen is some solids, like sand.) The heat
  moves with the fluid.
• Consider this convection is responsible for
  making macaroni rise and fall in a pot of heated
  water. The warmer portions of the water are less
  dense and therefore, they rise. Meanwhile, the
  cooler portions of the water fall because they
  are denser.

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RADIATION

• Radiation Electromagnetic waves that directly
  transport ENERGY through space.
• Sunlight is a form of radiation that is radiated
  through space to our planet without the aid of
  fluids or solids. The energy travels through
  nothingness! Just think of it! The sun transfers
  heat through 93 million miles of space.
• Because there are no solids (like a huge spoon)
  touching the sun and our planet, conduction is
  not responsible for bringing heat to Earth. Since
  there are no fluids (like air and water) in
  space, convection is not responsible for
  transferring the heat. Thus, radiation brings
  heat to our planet.

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Evaporation

• Makes use of the principles of conduction,
  convection and radiation.
• The evaporation of water requires heat which is
  provided by the body
• Even if a person is not sweating, water still
  evaporates from the skin

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Losing Heat

• Heat can be lost by the body through radiation,
  conduction, convection and evaporation

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Gaining heat and reducing heat loss

• The hypothalamus initiates two kinds of responses
  to balance any loss of heat.
• Some responses generate heat, others reduce the
  rate at which heat is lost from the body

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Heat production by Shivering

• Alternate contraction and relaxation of small
  muscle groups involuntary
• Activated by the hypothalamus
• When muscles shiver almost all the energy is
  converted into heat energy
• Drains energy reserves so cannot be sustained
  for long

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Heat production by metabolism

• Through a process of hormone production by the
  hypothalamus to the pituitary to the thyroid,
  thyroxine output is increased
• Thyroxine is a hormone that increases the
  metabolic rate of all cells of the body,
  resulting in an increase in heat production.

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Heat production by metabolism

• Motor nerves from the hypothalamus also cause
  the medulla of the adrenal glands to secrete
  adrenaline and noradrenaline.
• These hormones increase basal metabolic rate,
  particularly in skeletal muscles and brown fat

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Reducing heat loss through constriction of blood
flow in skin

• Constriction of arterioles to reduce heat loss
• Refer back to vasodilation and vasoconstriction

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Reducing heat loss through piloerection

• Hair standing on end
• Trapping a layer of air as a insulation layer
  between the skin and the external environment

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Behavioural activities for temperature regulation

• List as many as you can for humans heat loss,
  heat gain

In hot weather, kangaroos and wallabies often
lick their front legs. What benefit might this
behaviour produce?
Consider how a cat or dog sleeps in hot and cold
weather. How are they limiting or increasing
heat loss?
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Big or small which stays warm more easily?

• Consider both heat production and heat loss

Heat production in relation to the units of skin
surface
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Costs of Homeostasis
surface area to volume relationship heat is lost
through surfaces
as body size increases volume increases as a
power of 3 surface area increases as a power of
2
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Costs of Homeostasis
lower SA / V (big mammals) more precise
temperature regulation
less heat loss relative to thermal inertia of
organism