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MEDSCI second half > Thermoregulation in normal and extreme environments > Flashcards

Thermoregulation in normal and extreme environments Flashcards

1
Q

Many of the metabolic processes

essential to life produce ?

A

HEAT.

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2
Q

To maintain a constant body
temperature this HEAT must be
lost to the environment at a rate of?

A

that equals its production.

heat gain = heat loss

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3
Q

4 ways of Heat Gain

A 
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
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4
Q

4 ways of Heat Loss

A 
Conduction
e.g. touching a cold object
Convection
e.g. blood flow to skin
Evaporation
e.g. sweat
Radiation
e.g. skin to environment
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5
Q

rate of heat production is proportional to

A

metabolic rate

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6
Q

• Heat is

A

a spontaneous flow of energy from one object to
another caused by a difference in temperature between the
two objects.

Temperature is not heat

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7
Q

• Heat exists only as

A

energy in transit from one object to

another.

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8
Q

• When heat energy is added to a system, it is stored as

A

kinetic

energy of the atoms and molecules making up the system.

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9
Q

The Heat-Balance Equation

A

[metabolism (energy gained)– work (energy lost) ] - (heat loss) = storage of heat (Hs)

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10
Q

Storage heat formula:

A

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

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11
Q 
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
A

contact
minimal
conductivity

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12
Q
  1. 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
A

temperature gradient
density
convection
Clothing

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13
Q

Conduction eqn

A

Hcond. = κcond.A.(T2 – T1)
Heat transfer is dependent on thermal conductivity and the temp.
difference between the two objects

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14
Q

Convection eqn

A

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

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15
Q

Higher wind speeds ______convective heat loss
and the ‘_____’ temperature is lower than the
‘ambient/air’ temperature

A

increase

apparent

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16
Q
  1. 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)
A

respiratory
skin
water vapor pressure gradient

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17
Q

Evaporation eqn

A

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)
.

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18
Q

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.

A

sweat glands

cholinergic

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19
Q 
4. Radiation:
• Radiation is the transfer of
\_\_\_\_\_\_\_energy by means
of \_\_\_\_\_\_\_\_waves
(infrared).
• Radiation heat transfer
does NOT require a?
A

thermal
electromagnetic
material medium

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20
Q

4 physiological modes of thermoregulation (effectors):

A
  1. metabolism
  2. vasomotor regulation (blood flow)
  3. sweating
  4. shivering
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21
Q

2 main Thermal regions

A 
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’
22
Q

• Mean body temperature MBT eqn

A

MBT = 0.64Tcore + 0.36Tshell

23
Q

In females, core
temperature fluctuates with
the ?

A

menstrual cycle:
• hormone levels
• endometrial thickness
• ovulation

24
Q

Where is Heat Produced?
At Rest:
During Exercise:

A

primarily brain, heart,
liver and kidneys
primarily skeletal
muscles

25
Q

Where is Heat Produced?

A 
Overwhelmingly through the skin, via:
Radiation
Conduction
Convection &
Evaporation
26
Q

At normal ambient temperatures 50 – 65 % of the heat of metabolism is lost by ___, with most of the
remainder lost by evaporation.
In a cold environment, _______is the major source of heat loss (blood flow to the skin ↓s to prevent this)

A

radiation

convection

27
Q

Insulation of the shell
Qualitative Variation:
Quantitative Variation:

A 
(vary the medium)
• Fat (κcond = 1/3)
• Feathers
• Fur/Hair
• Behavioural (clothing)
(vary the thickness)
• “Winter fat”
• Piloerection (air-trapping)
• Variable blood-flow to the
skin (vasodilation &
vasoconstriction)
28
Q 
Thermoregulatory Control
Feedback System
Receptors 
Controller (Integrator)
Effectors
A 
R- SKIN, BRAIN
C- Hypothalamus
E-1 Metabolism
2. Vasomotor
3. Sweating
4. Shivering
29
Q 
Temperature sensors - receptors
Unlike many Negative
Feedback Systems,
there are two distinct
types of peripheral
(skin) sensors:
A 
Warm Receptors
&
Cold Receptors.
Afferents from these
receptors project to the
pre-optic hypothalamus
30
Q

Process of regulation of Heat transfer

A 
Peripheral (skin) thermoreceptors,
core thermoreceptors
• Input signal compared with ‘set
point’
• Effectors:
shivering, vasomotor, sweat
• Activate/deactivate heat transfer
31
Q

Metabolism Effector location

A

-Brown adipose

tissue, Mainly in newborns

32
Q

Vasomotor Effector location

A

Blood vessels
Vasoconstriction at skin,
vasodilation at core = heat
retention

33
Q

Sweat Effector location

A

Increased sweat leads to
evaporative heat loss in dry
environments

34
Q

Shivering Effector location

A

Increases metabolic heat

production

35
Q

Piloerection Effector location

A

Traps a layer of air between skin

and hair = insulation

36
Q 
Metabolic heat gain:
brown adipose tissue
‘brown fat’
high density of ?
situated close to ?
A

• Newborn humans & hibernating animals (possibly also sig. adult humans)
• High density of mitochondria for high level of metabolic activity
• Situated close to blood vessels so that heat produced by metabolism of
fatty acids can be quickly distributed to the rest of the body

37
Q

How is heat transferred

within the body?

A

Conduction

Advection/Convection

38
Q

Conduction speed?

Advection/Convection speed?

A

Conduction: SLOW

Advection/Convection: FAST

39
Q

Heat transfer through vasodilation
To remove heat produced by metabolism,
______is the primary mode of heat loss

A

convection

vasodiation

40
Q

Hyperthermia of exercise

At the onset of exercise:

A 
heat gain > heat loss = ↑ Tcore
The hypothalamic integrator:
Tcore ≠ Tset = “error” 
Neural output to activate heat loss
via skin blood flow and sweating
When heat loss = heat gain storage
of heat decreases to zero
But the elevated Tcore persists as
long as exercise is maintained.
41
Q

Heat stroke – a medical emergency

A

• Occurs when the thermoregulatory system fails and core
temperature increases to 41°C or above
• Excessive vasodilation at skin causes drop in blood pressure (&
decreased brain perfusion) – confusion, loss of consciousness
• Can be rapid in onset

42
Q

Heat stroke – a medical emergency

• Treatment

A 
is to sponge with tepid water (evaporative cooling)
\+ a fan (convective cooling)
• Only place ice packs over skin where
large vessels are near surface
(neck, under arms, groin
43
Q

Fever Hyperthermia

A

• Set point is raised (different from other types of hyperthermia)

44
Q

Fever Hyperthermia

• Caused by

A

cytokines from the immune system crossing the
blood-brain barrier which increases Tset
• Brain sends neural output to increase heat gain/retention to
increase Tcore to new higher Tset

45
Q

Therapeutic hypothermia

A

• Lowering core temp. can protect the brain from reperfusion
damage post-Stroke or cardiac arrest
• ↓ metabolism, reactive oxygen species, cell death, glutamate

46
Q

Heat exchange with the environment is used to regulate body temperature via:

A

– Conduction
– Convection
– Radiation
– Evaporation

47
Q

The body produces heat from

A

metabolism

48
Q

_____varies between people, throughout the day and with hormone level in
females

A

Tcore

49
Q

Thermoregulatory control system involves

A

receptors, the controller/integrator and

the effectors

50
Q

Fever hyperthermia is initiated by

A

an increase in Tset

51
Q

• Exercise hyperthermia involves a maintained increase in ?

A

Tcore

MEDSCI second half (10 decks)

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