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Physics of the human body > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

Temperature for hyperthermia

A

> 40 deg C

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2
Q

Temp for hypothermia

A

< 35

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3
Q

What reactions included in metabolism

A

chemical reacitons which sustain life

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4
Q

Catabolism

A

breakdown of molecules into smaller components
to release energy

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5
Q

Example of catabolism

A

protein –> amino acids
polysacchardies –> glucose

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6
Q

how is energy lost in catabolism?

A

lost as heat and ATP

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7
Q

what is ATP

A

a unit of energy storage

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8
Q

Anabolism

A

building up molecules
requires energy: making ATP from ADP

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9
Q

How is anabolism regulated?

A

Anabolic steroids, regulated by hormones

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10
Q

BMR

A

basal metabolic rate: the basic rate of breakdown of molecules to release energy

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11
Q

what processes make up the rate of breakdown of molecules in BMR?

A

catabolism (brekdown of molecules)
anabolism (build up of molecules)
maintenance of an ionic gradient
manufacturing of secretions and hormones
nerve impulses
minimum muscle activity

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12
Q

what is average BMR?

A

72kcal/h

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13
Q

How is BMR normalized?

A

divided by average body surface area = 1.8 m^ 2

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14
Q

Formula describing metabolism and the first law of thermodynamics

A

heat change in the body = change in internal energy (metabolism) - work done by the body

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15
Q

formula for internal energy

A

catabolic rate (rate of breakdown of molecules to release ATP)- measure from oxygen consumption

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16
Q

formula for change in heat added to the body

A

rate of heat production - measure from human calorimetry

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17
Q

formula for rate of change of work done by body

A

power delivered by body - measure from treadmill

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18
Q

what are the smaller effects changing heat added to the body across individuals?

A

weight loss/gain, excretion

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19
Q

What metabolic rates are included in the basal metabolism?

A

basal heat released from liver, brain, skeletal muscle and others

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20
Q

how much warmer are metabolically active organs?

A

1 deg C

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21
Q

How much of the energy in food is stored as ATP

A

50% lost as heat in production of ATP
45% stored as ATP

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22
Q

formula for energy released as heat production

A

temperature change x mass x specific heat capacity

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23
Q

what is the avg specific heat capacity of the body?

A

3500

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24
Q

Q = heat production at BMR = 80 W
body mass = 75kg
specific heat capacity of the body = 3500
rate of temperature increase?

A

80 W = 80 J / s
in 1 hour total heat energy released = 80 x 3600s
rate of temperature increase as deg C / hour
80 x 3600 / 75 x 3500 = 1 deg C / hour

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25
Q

What is conduction?

A

a form of heat loss
direct transfer of heat energy between vibrating molecules in contact

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26
Q

What is fourier’s law?

A

the rate of heat transfer is proportional to temperature gradient and area through which the heat flows is perpendicular to the gradient

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27
Q

mathematical formula for the rate of heat transfer in conduction

A
  • constant of thermal conductivity x crosssectional surface area x temperature gradient (degrees C / metre )
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28
Q

2 most important methods of conduction?

A

direct conduction to objects
conduction within the body

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29
Q

Direct conduction to objects

A

generally a small effect, contributing to 3% of the total heat loss. Most of the body is insulated by clothes so direct conduction doesn’t occur very frequently

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30
Q

how to decide which thermal conductivity constant to use for 2 directly conducting objects ?

A

use the k for the object that is generating heat

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31
Q

Conduction within the body

A

minimal as the rate of temperature change with respect to distance tends to 0 – the temperature difference between 2 neighbouring areas is very small

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32
Q

How is heat mainly transferred in the body?

A

by blood

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33
Q

How to calculate the heat loss from conduction within the body?

A

Model the body as a series of geometric shapes
In practice, use finite element modeling

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34
Q

Convection

A

bulk movement of heated fluids

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35
Q

Newton’s Law of Cooling

A

the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings

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36
Q

compare conduction and convection

A

more complex than conduction

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37
Q

what does the rate of convection depend on?

A

dimensions, properties of fluids involved (density, viscosity, specific heat capacity, velocity), temperature, conduction of heat to surface

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38
Q

2 types of convection

A

free
forced

39
Q

Free convection

A

Warm body causes temperature and desntiy gradients in stationary fluid

40
Q

Forced convection

A

Relative movement between body and fluid
No sharp boundary between free and forced convection
Depends on many effects

41
Q

Radiation

A

Any object with temperature T radiates according to the Stefan-Boltzmann Law

42
Q

Maximum wavelength of radiation emitted by skin

A

9000nm

43
Q

Type of radiation from human body

A

infrared

44
Q

emissivity of human body at normal wavelengths

A

0.97

45
Q

Evaporation methods

A

sweat secretion, sweat secretion (to moist air, forced to moist air), respiration

46
Q

factors affecting the latent heat of evaporation

A

temperature and pressure

47
Q

How does pressure affect the rate of evaporation?

A

higher pressure gradient, higher rate of evaporation

48
Q

Diffusion of water through the skin

A

water leaks passively through skin
insensible water loss
independent of exercise and sweating

49
Q

what does the rate of water loss depend on

A

the difference between the partial pressure of water at the skinand the partial pressure of water in the ambient air

50
Q

What condition for sweating to occur?

A

activity > BMR

51
Q

how does sweat lead to energy loss?

A

sweat is turned to vapour
evaporation process requires energy

52
Q

Assumption in calculations for heat lost in sweat secretion

A

no sweat is lost as liquid, and all the sweat evaporates freely into dry air

53
Q

Sweat secretion to moist air compared to dry air

A

less efficient

54
Q

Partial pressure

A

pressure that one gas in a mixture of gases would have if it alone occupied the volume

55
Q

Forced sweat secretion to moist air

A

Sweating often takes place in moving air
It has the same effect as convection
It is the dominant source of heat loss during exercise

56
Q

Factors affecting rate of sweat secretion to moist air

A

partial pressure due to water at surface - partial pressure due to water at ambient pressure

57
Q

calculate rate of respiration

A

include calculations in heat loss due to heating air and due to evaporation from process of inhalation and exhalation

58
Q

Counter current mechanism

A

to minimise a gradient
Condition: ambient temperature is cold, hot blood goes to skin and is cooled leading to significant hat loss
as the blood leaves the core (warm) it mixes with blood that is coming back from the skin (cold)
the process is where heat exchange happens across neighbouring vessels continually, in which the blood flow directions are opposite (going away from core vs. going to core)

59
Q
A
60
Q
A
61
Q

How is core temperature measured ?

A

peripheral and core thermoreceptors. Integrated and regulated by preoptic region of hypothalamus

62
Q

2 types of mechanisms for core temperature control

A

linear control
on-off control

63
Q

how does the hypothalamus work to control temperature

A

sets a desired reference temperature and can feed-forward to counter expected changes in core temperature

64
Q

Type of feedback that metabolic rate experiences

A

positive

65
Q

Types of temperature receptors

A

warm and cold receptors

66
Q

firing rates of warm vs cold receptors

A

firing rate increases with temperature in warm receptors
firing rate decreases with temperature increase in cold receptors

67
Q

Thermoregulation in the neonate

A

Full-term newborn can thermoregulate if kept dressed in a warm room, pre-term cannot

68
Q

why do newborns have lower ability to thermoregulation?

A

immature skin –> increased water loss
big surface area : volume ratio
immature vasculature –> limited vasocontriction to draw blood away from the surface of the skin
little fat –> poor heat insulation
unable to shiver due to less muscle

69
Q

how are premature babies protected from poor thermoregulation?

A

heated incubator
wrapped in plastic
wear a hat
radiant heater
heated mattress

70
Q

neural thermal environment

A

no energy required to be expended to maintain body temperature, so more energy available to grow

71
Q

examples of neutral thermal environment

A

premature babies incubator, womb

72
Q

brown fat in term babies

A

metabolically active fat which contains mitochondria

73
Q

where is brown fat found

A

term babies, hibernating animals

74
Q

cold-blooded vs warm blooded animals

A

variable vs stably maintained body temperature
body temperature varied externally vs by varying rate of metabolism
metabolism is maintained at high vs metabolism varied for reasons other than thermoregulation e.g reproduction

75
Q

advantages of cold blood

A

lower energy requirements

76
Q

disadvantages of cold blood

A

lower efficiency
cannot engage in high-energy activities

77
Q

Types of response to hot conditions

A

fever, hyperthermia, heat exposure, heatstroke

78
Q

when does fever occur?

A

when the set-point is increased by the hypothalamus and normal regulatory mechanisms maintain body temperature at this higher level to destroy pathogens

79
Q

Hyperthermia

A

increased body temperature due to failure of autoregulation due to high ambient temperature, side-effect of metabolism increasing drugs

80
Q

heat exposure

A

leads to hot flushed skin heavy sweating, dizziness, fatiugue, mental confusion

81
Q

heatstroke

A

body temperature is above 40
failure in homeostasis
autoregulation fails
metabolism increases with temperature increase
leading to positive feedback

82
Q

Areas in a burn

A

zone of coagulation
zone of stasis
zone of hyperaemia

83
Q

Zone of coagulation

A

center of the burn
maximum damage due to proteins denatured
irreversible

84
Q

Zone of stasis

A

Reduced perfusion
damaged but not destroyed cells

85
Q

Zone of hyperaemia

A

minimal cell injury

86
Q

Adjuvant hyperthermia therapy

A

physiological hyperthermia
adjuvant hyperthermia

87
Q

physiological hyperthermia

A

mild heating for long time periods
leads to increased metabolism

88
Q

adjuvant hyperthermia

A

treat cancer
tumour cells have altered surface so lower ability to thermoregulate
increases the radiosensitivity of the tumour cells to chemotherapy

89
Q

Ablative hyperthermia therapy

A

High intensity focussed ultrasound
destroys cells in few mm cubed tissue to denature the protein and allow coagulation

90
Q

Formula for net heat exchange assuming all heat exchange is radiated

A

net heat exchange = conductivity x emissivity of the source x effective area x temperature change

91
Q

what is the specific heat capacity of water?

A

4200

92
Q

what is the emissivity of human skin

A

0.97

93
Q

what is the conductivity of skin

A

8

94
Q
A

Physics of the human body (5 decks)

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