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HOM > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

Are humans homeotherms

A

Yes - they employ physiological as well as behavioural means to keep core body temperature within a narrow range

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2
Q

Are muscles 100% efficient

A

No - a high proportion of energy is lost as heat

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3
Q

How do humans utilise evaporation to lose heat

A

Panting

Sweating

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4
Q

How good is sweat at removing heat

A

Every gram of sweat evaporated removed 2.45kJ of heat

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5
Q

What kind of system is thermo regulation

A

Homoeostatic negative feedback system with feedforward control

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6
Q

Name 3 key areas involved in thermoregulation

A

Median preoptic sub nucleus
Median preoptic area
Lateral parabrachial nucleus

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7
Q

What is temperature change

A

The difference between heat production, heat gain and heat loss (measured in watts) divided by the heat capacity of the system

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8
Q

Show rate of temperature change as an equation

A

Production+gain-loss
———————————-
Thermal mass

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9
Q

What are the units used for the following:
a) Rate of change in temperature

b) Heat gain
c) heat loss
d) Thermal mass

A

a) Degrees C per second
b) Watts
c) Watts
d) J/ Degrees C

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10
Q

What is endothermy

A

Internal generation of heat

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11
Q

Give two advantages and disadvantages of being an endotherm

A

Advantages: gives organism speed and independence from the environment

Disadvantage: requires considerable energy input
When the heat production is greater than required to stay warm a great deal of water can be needed

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12
Q

What is the source of heat in endotherms

A

Metabolism – the moment metabolic clique active a tissue, the more heat is generated

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13
Q

Using 1 L of oxygen to break down carbohydrates yields how much energy?

A

20 kJ or 4.8 kcal

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14
Q

How much heat does the average sized human produce

How much energy does this amount to

A

80 W at resT

70 kcal/h or 1600 kcal per day

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15
Q

80 W is sufficient power to raise how much water by 1° per hour

A

70 kg

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16
Q

What happens if you fully insulate a person who is not moving

What does this mean for warming up a cold person

A

The temperature will rise by 1° C per hour

Simply insulating them and waiting for them to warm up is not a good strategy
it could take longer than 10 hours to raise their temperature by 10°

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17
Q

At rest, how much of the heat generated by the body is generated by the brain

What about muscles and skin at rest

General viscera?

A

1/6

1/6

1/2

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18
Q

1 L of oxygen consumed releases how much energy

A

20 kJ

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19
Q

How does temperature affect memory

A

Cooling of just 1° C can impairment memory

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20
Q

What happens if the brain is warmed by a few degrees C

A

Confusion and nausea arise

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21
Q

Which is the most temperature sensitive organ

A

The brain

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22
Q

When is brain cooling used

A

When brain damage has occurred or blood circulation is compromised

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23
Q

How does fetal oxygen deficiency and life expectancy relate to temperature

A

Survival improves if hypothermia is induced

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24
Q

What is being used by adults during chemotherapy to prevent hair loss

How does this work

A

Cool caps

The cooling lowers the metabolic rate of the cells that produce hair and this lowers the toxicity of the drugs

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25
Q

What is the optimal temperature for the heart

It will continue to pump until which lower Boundry

A

38° C

25° C

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26
Q

What temperature a heart for heart transplants start in

A

Just a few degrees C

Contraction stop until the solution is replaced by blood and the heart is rewarmed

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27
Q

What will happen if the heart goes below 25° C

A

The heart will stop beating and the subsequent lack of blood flow to the brain will kill you

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28
Q

Describe the experiments by Starling to investigate the temperature sensitivity of the heart

A

He used hearts isolated from dogs and cats to share that cardiac output varies a temperature

At about 44° C the heart stops pumping. Above the temperature of the heart undergoes irreversible damage which is colloquially known as cooking

Below 25° say the heart stops. Whilst the damage caused by heating is irreversible hearts that have been called can often be restarted when rewarmed

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29
Q

Which phrase comes from the fact that a cold heart can restart when rewarmed

A

No one is dead until they are warm and dead

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30
Q

What is the best temperature for skeletal muscle function

Why is this a good thing

A

Slightly warmer than normal core body temperature

When they are active they produce a lot of heat

cool skeletal muscle produces less force, moves more slowly and produces less power

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31
Q

How does the power of skeletal muscle change between being at 10° and 20°C

A

The power increases by 10 times

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32
Q

What temperature it to the testes function best at

A

35 or 34° C

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33
Q

How do you temperatures of 40° affect fertility

A

Can lead to temporary infertility

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34
Q

Does heat stress only affect male reproductive organs?

A

Work on Dairy cattle shows that heat stress affects reproductive performance of both sexes

This may not be a direct effect of heat but the effect of the thermoregulatory stress that the heat causes

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35
Q

How temperature sensitive is the skin

Why is this

A

It can function over a very wide range of temperatures

At the lower end sensation becomes lost and at the higher end there may be pain

The skin form is one of the thermal layers that sits between the heat generation mechanisms within the organism and the external environment. It is responsible for a lot of thermoregulation and so often suffers from large swings in temperature

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36
Q

How can you think of the distribution of the temperature in an organism

A

Like an onion but less uniform

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37
Q

What is the core temperature of most endotherm is represented by

A

The temperature of the arterial blood

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38
Q

Why is the organism mean temperature important

A

It governs the potential swings and temperature that are possible as bloodflow changes

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39
Q

What is the warmest part of the body

A

The core temperature except when doing physical exercise

It would then be skeletal muscle

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40
Q

When is the thermal gradient between skin and core temperatures highest and lowest?

A

Highest: in cold conditions
Lowest: in warm conditions

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41
Q

How would a patient hand appear if they had Raynaud’s syndrome

A

Very cold fingers (below room temperature)

This arises from poor bloodflow and sensation can be compromised

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42
Q

In a thermal vision image a calf will have patches of red and yellow around the body. What is this?

A

Underlying brown fat

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43
Q

How does our core temperature vary over a 24 hour cycle

A

It is typically coolest around 4 am and highest in the early afternoon

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44
Q

How much can exercise a warm an individuals core

A

3° C

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45
Q

Name three cycles which causes temperature variation

A

Diurnal variation

Menstrual cycle

Seasonal cycle

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46
Q

What is the worst way to obtain a core body temperature

Why

A

Oral/sublingual

Airflow through the mouth affects temperature reading

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47
Q

How accurate is axillary temperature measurement

A

Not very

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48
Q

What is a new popular form of testing core body temperature

A

Tympanic measurements with an infrared thermometer

They are quick and easy but hard to perform reliably and not very accurate

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49
Q

What are the only two really good ways to test core temperature

A

Oesophageal/intestinal with either a probe or temperature broadcasting pill

Or

Rectal measurement

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50
Q

What is the Boltzman constant

What does this mean

A

1x10^-23 J/K/ molecule

One mole of molecules has an energy content of 8.3 J per Calvin

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51
Q

How much energy does each mole have at 37° C

A

2.6 kJ per mole

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52
Q

Why is it important that at 37° C it molecules have 2.6 kJ per mole?

A

This is not enough energy to break carbon carbon bonds so proteins and other organic compounds are stable

However it is enough to break Van de Waal’s interactions to enzymes can work

37° C is therefore a good temperature because it renders a molecule sufficiently but not too energetic

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53
Q

What does it mean to say a biological reaction has a Q10 of two

A

They increase their rate by two times for a 10° C rise

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54
Q

What is the Q10 of most biological reactions

A

Two or three

55
Q

What happens if the body temperature gets too low

A

Not enough energy is provided

Proteins and lipids are too inflexible

Organs can be slowed to a stop

56
Q

What happens if the body temperature gets too high

A

Proteins denature

Membranes too flexible

Metabolic rate too high

57
Q

How high are the body temperatures of birds

A

42 in the light

58
Q

Compare the temperature fluctuations of camels when hydrated and dehydrated

Why is this

A

Hydrated: fluctuation of 3° C throughout the day

Dehydrated: fluctuation of 6° C throughout the day

The camel is trying to reduce the need for a relative cooling with water by starting with a lower court temperature in the morning and allowing its core temperature to rise more during the day. It can then radiate out heat without losing water at night.

59
Q

What is hibernation

A

A strategy to reduce the energy required to stay warm

It is a period of reduced metabolism and body temperature during the winter.

60
Q

How low can cause temperatures fall during hibernation

How long can hibernation last

A

To only 1° C

For months

61
Q

What is a shorter term response that can be compared to hibernation

A

Torpor

When animals such as hummingbirds are in active but not actually asleep

62
Q

Do bears hibernate?

A

They have a period of winter lethargy (Denning) where there core temperature drops from which they can awake nearly instantly

This is not hibernation however as the temperature drops for less than true hibernators (<10 degree drop)

63
Q

What is the survival rate if humans call body temperature reaches 41.5° C

A

50%

This dropped even lower if you reach 42° C

64
Q

What is the main cause of death during the heat wave

A

Haemoconcentration

This causes thrombosis and heart attacks

Heat stress doesn’t usually result in death through overheating but rather the effects of Thermoregulation – sweating

65
Q

How many XS winter deaths are there each year on average

What does this mean

A

26,000

Cold weather is indirectly responsible for about 5% of deaths

66
Q

Why does cold weather in directly lead to increased death

A

Impaired mobility

Circular Tory Phalia

Diseases e.g. flu

Increase viscosity of blood is seen in the cold

67
Q

What is perniosis?

How can it be avoided

A

Chilblains

Cold exposure or rapid warming following cold damages capillary beds in the skin which causes redness, itching, blisters and inflammation

Appropriate insulation

68
Q

What happens in frostbite

A

Not just capillaries are damaged but the underlying tissue to and the cells are broken apart by ice crystal formation

69
Q

Where are the thermoregulatory inputs integrated

A

In the preoptic area of the hypothalamus

70
Q

What are the Thermo receptors

How do they work

A

Both warm and cold sensitive nerve fibres found in the skin

They respond to relative temperature changes

Warm fibres increased discharge above 37° C
Cold fibres increased discharge below 37° C

However noxious heat is capable of activating cold fibres

71
Q

Which channel type underlies the action potential firing of Thermo receptors

A

TRP (Transient receptor potential)

72
Q

Which ion channels are activated by an increase in temperature

Above which temperature are they usually activated

A

TRP-V1
TRP-V2
TRP-V3

Above 30° C

73
Q

Which channel is activated by cold

A

TRP-M8

74
Q

What can activate TRP – M8

A

Temperature is below 25° C

menthol

75
Q

Are the TRPM8 channels only useful for temperature regulation

A

They also Have a role in regulating eating behaviour and fuel utilisation

Knock out mice will get fat

76
Q

Does the actual temperature of the hypothalamus affect heat regulation

A

Yes

If the hypothalamus is heated above a certain temperature, cooling mechanisms become activated and vice versa

77
Q

Describe brown adipose tissue

A

Similar to skeletal muscle without the contractile proteins

It is rich in blood vessels and mitochondria

Its activation underlies nonshivering thermogenesis

78
Q

What activates brown adipose tissue

A

Noradrenaline released from sympathetic nerves under hypothalamic control

79
Q

How much of the body weight of a newborn calf is estimated to be brown adipose tissue

A

2%

80
Q

How much energy can brown adipose tissue produce

A

300 W per kilogram

81
Q

What makes mice a poor model for humans

How might we overcome this

A

The dominant role of brown adipose tissue as an energy consumer

Keep the mice in warm conditions (30° C)

82
Q

What protein gives brown adipose tissue the ability to generate heat

A

UPC1 in mitochondria

83
Q

What does UPC1 do

A

Allows H+ to leak out of mitochondria

This allows the electron transport chain to operate unhindered, making the mitochondria inefficient and generating lots of heat

84
Q

Briefly describe the molecular mechanism behind UCP1

A

There is a binding of the long chain fatty acids to UCP1 producing a complex capable of transporting proteins

85
Q

Which receptor activates brown adipose tissue

Why might these receptors be activated

A

β-3 adrenergic receptors

In low nutrient Content diets were brown adipose tissue may help burn off excess calories

86
Q

How fast does skeletal muscle contract when shivering

A

200Hz Isolation

87
Q

True or false:

Shivering is more powerful in individuals who are chronically exposed to cold

A

False

Shivering tends to be lost as a response in these patients as other production mechanisms are up regulated

88
Q

What is malignant hyperthermia

A

A single point mutation of the ryanodine receptor

The receptor becomes spontaneously active causing XS muscle contractions, resulting in large muscles

89
Q

How can malignant hyperthermia be treated

A

Active cooling can delay death

Dantrolene is the only effective treatment

90
Q

What are the issues with dantrolene?

A

It is hard to prepare and not very water-soluble

It is pH 9.5

91
Q

Which hormone is up regulated in response to chronic cold

A

Thyroxine

This is a powerful way of regulating general heat production

92
Q

Name three physiological controls of heat loss in humans

A

Bloodflow

Piloerection

Sweating (panting in other mammals)

93
Q

What are our three ways of losing heat

A

Radiation

Conduction

Evaporation

94
Q

In a cool room how do we lose most of our heat

A

Radiation

95
Q

What happens if the walls of a room are above body temperature

A

Radiation only results in heat gain

96
Q

Discuss the specific heat capacity of air, stone, and water

What does this mean

A

Air: Low

Stone: high

water: high

Solid floors and water are very good ways of losing heat via conduction
Heat is also lost through water via convection

97
Q

True or false

Even in what feels like Warm water we can lose the equivalent amount of heat as our BMR

A

True

98
Q

What is glabrous skin

Where is it found

Describe its role in Thermoregulation

A

Hairless skin

On the palms of the hands and face

It does not play a major role in some regulation But they are rich and arteriovenous anastomoses which can bypass the high resistance capillary bed

99
Q

What is the innovation of apical skin

A

Sympathetic vasoconstrictor fibres

100
Q

What are the two sympathetic innervations of hairy skin

A

Vasoconstrictor

Sympathetic vasodilator (cholinergic)

101
Q

What is the normal thermoregulatory pathway in hairy skin

What about in hairy skin during high core temperatures

A

The vasoconstrictor nerve supply

The vasodilator pathway

102
Q

Normal resting bloodflow to the skin is ___?

A

Low

103
Q

What must occur with sweating for heat loss to continue

A

Increased skin blood flow

104
Q

How does piloerection work

A

Small muscles at the base of hair follicles change the angle of the hair to the skin to trap air or provide defence advantages

105
Q

What is the most powerful source of heat loss from the skin

How much energy can this lose

A

Evaporation of water

2500 kJ/L of water

106
Q

What are the two major sites of evaporation

A

Skin or respiratory surfaces

107
Q

Why is panting better than sweating

A

Starting from the skin result in salt loss and requires airflow – panting does not

108
Q

What is a disadvantage of panting

How can this be overcome

A

It produces muscular heat and can alter arterial pCO2

Shallow panting can minimise alkalosis by ensuring that most of the ventilation is in the upper respiratory dead space.
Muscular work can be minimised by panting at the natural resonant frequency of the respiratory system

109
Q

What is the natural resident frequency of the respiratory system of a dog

A

5Hz

110
Q

Do birds pant or sweat

A

They have a form of panting called gular flutter

111
Q

What does panting provide that sweating does not

A

The ability to cool the brain selectively through a structure known as the rete mirabile

112
Q

What is the rete mirabilia?

A

A structure where veins returning cooled blood from nasal passages are associated with the arterial vessels supplying the brain

This network allows heat transfer and a cooler brain than the core

Rete mirabilia also occur in the blood supplying the testes and feet

113
Q

What are the malodorous sweat glands

A

Apocrine

114
Q

What do eccrine sweat glands produce

A

A weakly salty solution used in Thermoregulation

115
Q

What are the dimensions of an eccrine sweat gland

A

40μm in diameter

Several mm long (longer in people who sweat more)

They are coiled tubes formed from a polarised epithelium with a tubular lumen

116
Q

What triggers sweating

A

Sympathetic cholinergic innervation – the sudomotor nerves

117
Q

Which Ion transporter plays an important role in sweat production

How

A

The Na-K-Cl2

The secretion produced at the base of a sweat gland is modified by this transporter as it flows to the surface and salt is removed

118
Q

How complete is the removal of sodium from the initial secretion in eccrine sweat glands

A

At a low flow rate it is almost complete (5mM NaCl)

At higher rate, this fact is saltier – still hypotonic but the salt loss is significant (60mM)

119
Q

How can you train your sweat glands to produce more sweat

What can do the opposite

A

Heat acclimation and aerobic training

Bed rest

120
Q

What kind of people produce more sweat

A

Fitter/trained people are able to produce more sweat earlier during exercise

121
Q

What makes elderly people particularly susceptible to both overheating and haemoconcentration in heatwaves?

A

The detraining of sweat glands by failure to exercise

122
Q

What is the difference in sweat responses between men and women

A

The only difference is fitter individuals sweat more because they can produce more muscular power

However women are still at more risk than men of the heat simply because they are typically smaller and less powerful so their sweat glands have been trained less by normal heat stress

123
Q

What is pyrexia

A

Fever

124
Q

What causes fever

A

Infection
Pyrogens
Prostaglandin E2

125
Q

What stimulates the production of prostaglandin E2

Where is it secreted from

A

Pyrogens

endothelial cells in small venules of the hypothalamus

126
Q

What does prostaglandin E2 do

A

Raises the point at which cooling mechanisms are activated

127
Q

What is the symptom of a fever

A

A feeling of cold in a Thermoneutral environment

128
Q

Name an anti fever drug

A

NSAID drugs block PGE2 and are thus antipyrexic

129
Q

Why do infections cause fever

A

They are exogenous pyrogens that activate white blood cells to produce endogenous pyrogens and activate the hypothalamic endothelium to produce PGE2 and raise the set point

130
Q

Why are fevers clinically useful

A

Diagnostically – useful sign of presence of infection and effectiveness of treatment

Also indicate the need for rest and reduce desire to perform intense exercise that might be dangerous e.g. endocarditis

131
Q

How was Fever used to cure syphilis

A

Malaria could be controlled with quinine

Malaria caused fever

Infecting a patient who had syphilis with malaria caused a fever that killed the bacteria causing syphilis

132
Q

Give the different definitions for organisms based on how they thermoregulate

A

Homeotherm- body temperature above environment (best avoided)

Poikilotherm - changeable temperature/ “cold blooded” (again best avoided)

Endotherm- Able to maintain a high body temperature by internal heat production

Heterotherm – mostly have a high regulated body temperature but can cool down

133
Q

How would you define a hibernating mammal?

A

Heterothermic endotherm

HOM (11 decks)

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