Thermoregulation in normal and extreme environments Flashcards
(51 cards)
Many of the metabolic processes
essential to life produce ?
HEAT.
To maintain a constant body
temperature this HEAT must be
lost to the environment at a rate of?
that equals its production.
heat gain = heat loss
4 ways of Heat Gain
Conduction e.g. touching a hot object Convection e.g. from a fan heater Metabolism e.g. basal, digestion, exercise Radiation e.g. from the sun
4 ways of Heat Loss
Conduction e.g. touching a cold object Convection e.g. blood flow to skin Evaporation e.g. sweat Radiation e.g. skin to environment
rate of heat production is proportional to
metabolic rate
• Heat is
a spontaneous flow of energy from one object to
another caused by a difference in temperature between the
two objects.
Temperature is not heat
• Heat exists only as
energy in transit from one object to
another.
• When heat energy is added to a system, it is stored as
kinetic
energy of the atoms and molecules making up the system.
The Heat-Balance Equation
[metabolism (energy gained)– work (energy lost) ] - (heat loss) = storage of heat (Hs)
Storage heat formula:
Hstorage = ctissue .x massbody .x ΔTempbody
c= specific heat capacity
is the amount of heat energy required to raise the
temperature of 1kg mass by 1 Kelvin
1. Conduction • Heat energy is transferred through a solid, liquid or gas by direct \_\_\_\_\_ • Under normal circumstances, heat gain or loss by conduction is \_\_\_\_\_ • Depends on the thermal \_\_\_\_\_\_\_of the materials in contact
contact
minimal
conductivity
- Convection
• Convection transfers heat by
fluid movement driven by a
__________
Transfer of heat from skin to fluid (air or H2O) warms the fluid,
thereby reducing its ______; it rises and is replaced by cooler
fluid.
• Air has a low specific heat capacity. It warms rapidly, establishing ______-currents.
_______impedes convection
temperature gradient
density
convection
Clothing
Conduction eqn
Hcond. = κcond.A.(T2 – T1)
Heat transfer is dependent on thermal conductivity and the temp.
difference between the two objects
Convection eqn
Hconv. = κconv.A.(T2 – T1) .
κconv. Is the convection coefficient W m-2 K-1
A = surface area
T = temperature of object 1 and 2
Higher wind speeds ______convective heat loss
and the ‘_____’ temperature is lower than the
‘ambient/air’ temperature
increase
apparent
- Evaporation
•Heat is continually transferred to
the environment as water is
vapourized from the ______
passages & the ____surface.
Evaporative heat transfer is dependent on the __________________ between the solution and the environment
(Note: partial pressure is dependent on temperature)
respiratory
skin
water vapor pressure gradient
Evaporation eqn
Hevap. = ĸevap.A.(P2 – P1)
Where:
• ĸevaporation = evaporation coefficient (W m-2 kPa-1)
• A = surface area available for heat exchange
• P = partial pressure of the evaporating fluid (usually H2O)
at a specified temperature (kPa)
.
The body has 2-4 million ____ ______throughout the surface.
• These eccrine glands are controlled by _______nerves &
secrete large quantities of weakly saline solution (hypotonic 0.2 – 0.4% NaCl).
• Cooling effect occurs as sweat evaporates.
sweat glands
cholinergic
4. Radiation: • Radiation is the transfer of \_\_\_\_\_\_\_energy by means of \_\_\_\_\_\_\_\_waves (infrared). • Radiation heat transfer does NOT require a?
thermal
electromagnetic
material medium
4 physiological modes of thermoregulation (effectors):
- metabolism
- vasomotor regulation (blood flow)
- sweating
- shivering
2 main Thermal regions
Core temperature - tightly maintained • Shell or skin temperature - highly variable • The core expands in a hot environment and contracts in a cold environment. • Changes to the shell vary the thickness of the ‘insulation’
• Mean body temperature MBT eqn
MBT = 0.64Tcore + 0.36Tshell
In females, core
temperature fluctuates with
the ?
menstrual cycle:
• hormone levels
• endometrial thickness
• ovulation
Where is Heat Produced?
At Rest:
During Exercise:
primarily brain, heart,
liver and kidneys
primarily skeletal
muscles
