Detecting Temperature Change
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
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
External temperature
change
If there is an increase in skin
temperature, the heat receptors increase
their rate of discharge along the affector
neurons
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
Hypothalamus
The temperature control centre of the body
Mechanism of Thermoregulation
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
37°C
Draw a negative feedback loop for
temperature change
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.
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.
Maintaining Core Temperature
Ways of gaining heat Ways of losing heat
Basic metabolic
processes
Shivering
Evaporation of sweat
Exercise or other
muscular activity
Radiation and
conduction to the body
Convection
Panting
Radiation and
conduction from the
body
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.
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.
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.
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.
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
Losing Heat
Heat can be lost by the body through
radiation, conduction, convection and
evaporation
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
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
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.
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
Reducing heat loss through
constriction of blood flow in skin
Constriction of arterioles to reduce heat
loss
Refer back to vasodilation and
vasoconstriction
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
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?
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
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
Costs of Homeostasis
lower SA / V (big mammals) = more precise
temperature regulation
less heat loss relative to thermal inertia of
organism