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Physiology > Thermoreceptors > Flashcards

Thermoreceptors Flashcards

1
Q

What does the hypothalamus control? x 7

A
  • body temperature,
  • thirst,
  • hunger,
  • water balance,
  • sexual function.
  • closely connected with emotional activity
  • sleep
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2
Q

What is external work?

A

energy used to contract skeletal muscles eg to move an object, or move the body in relation to the environment.

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3
Q

What is internal work?

A

1) all other biological expenditure that does not accomplish work outside the body eg contractions associated with postural maintenance or shivering
2) All energy expending activities necessary to sustain life eg Breathing, pumping blood etc.

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4
Q

How to calculate metabolic rate?

A

energy expenditure / unit of time

Units = kcal/hour (kJ/hour)

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5
Q

What is the basic unit of heat energy?

A

Calorie

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6
Q

What is a calorie?

A

The amount of heat required to raise the temperature of 1g of water by 1oC.

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7
Q

What conditions is the basal metabolic rate measured under?

A 
– Awake 
– Relaxed 
– Mental Rest (>30 min) 
– Lying 
– Warm (temp 20-25ºC)
– Fasting (12 hr)
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8
Q

There is a direct relationship between the volume of O2 utilised and the …..

A

Amount of heat produced

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9
Q

How to calculate the metabolic rate?

A

x L/hr x 4.8

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10
Q

What is food intake controlled primarily by?

A

Hypothalamus

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11
Q

What is the arcuate nucleus responsible for control of?

A
  • Long term control of energy balance and body weight

* Short term control of food intake on a meal to meal basis

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12
Q

How many subunits does the arcuate nucleus have?

A

2

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13
Q

What do the 2 subunits of the arcuate nucleus release?

A

One - neuropeptide Y

Other - melanocortins

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14
Q

What is neuropeptide Y?

A

An appetite stimulator

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15
Q

What is melanocortin?

A

An appetite supressor

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16
Q

What are the hormones secreted by adipocytes called?

A

Adipokines

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17
Q

Leptin, release, function

A

Released from stored fat, suppressed appetite, dominant long-term regulator of energy balance and body weight.

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18
Q

Which adipokines is suppressed in obesity?

A

Adiponectin

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19
Q

Function of adiponectin x 4

A
  • Promotes fatty acid oxidation by muscle
  • Increases sensitivity to insulin
  • Decreases body weight by increasing energy expenditure
  • Anti-inflammatory actions.
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20
Q

What adipokine is released primarily in obesity?

A

Resistin

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21
Q

What does resistin release lead to?

A

Insulin resistance

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22
Q

What is visfatin primarily released from?

A

From visceral fat

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23
Q

Function of visfatin

A

Stimulates glucose uptake; binds with insulin receptor at a site distinct from the insulin-binding site

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24
Q

Function of tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6)

A

Promote low-level inflammation in fat and throughout the body.

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25
Q

Neuropeptide source, effect

A

Source - arcuate nucleus of hypothalamus

Increases appetite

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26
Q

Melanocortins source, effect

A

Arcuate nucleus of hypothalamus

Decreases appetite

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27
Q

Leptin source, effect

A

Adipose tissue

Decreases appetite

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28
Q

Insulin source, effect

A

Source - endocrine pancreas

Decreases appetite

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29
Q

Ghrelin source, effect

A

Stomach

Increases appetite

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30
Q

Child with mutation of leptin gene before lepsin

A

Obeses

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31
Q

Core body temperature (tc)

A

Temperature within the inner core which consists of the abdominal and thoracic organs, CNS, skeletal muscles.

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32
Q

Causes of variation in core body temperature

A
  • Diurnal variation - 1C- lowest in early morning, highest in late afternoon
  • Menstrual cycle - +.5C last half
  • Exercise - increased
  • Age - elderly lower
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33
Q

Outer shell temperature

A

Comprised of the skin and body fat, the temperature of the outer shell is generally cooler and can vary substantially.

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34
Q

What can the skin temperature fluctuate between without causing damage?

A

Between 20°C and 40°C

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35
Q

What does an increase in temp do to cellular reactions?

A

Speeds up cellular chemical reactions

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36
Q

Nerve impact of temp increase

A

Nerve malfunction, irreversible protein denaturation

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37
Q

41° prob

A

Convulsions

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38
Q

43°C for body

A

Upper limit compatible with life

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39
Q

Decrease in temp on cellular reactions

A

Slows down cellular reactions

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40
Q

What does pronounced, prolonged fall in body temperature do?

A

Slows metabolism to fatal level

41
Q

Heat input and heat output

A

Heat input must balance heat output to maintain stable core temperature

42
Q

Heat input

A

– Internal heat production (Metabolism, Muscle)

– Heat gain from external environment

43
Q

Heat output

A

Heat loss from exposed body surfaces to the external environment

44
Q

Temperature control

A
  • If core temperature ↓ heat production is increased

* If core temperature ↑ heat loss is increased, and heat production is reduced

45
Q

What are the 4 mechanisms of heat exchange?

A
  1. Radiation (Heat waves)
  2. Conduction (Contact)
  3. Convection (Air)
  4. Evaporation (Sweat)
46
Q

Radiation heat gain/loss?

A

Heat gain and loss

47
Q

Conduction heat gain/loss?

A

Heat gain and loss

48
Q

Convection heat gain/loss?

A

Heat loss

49
Q

Evaporation heat gain/loss?

A

Heat loss

50
Q

What is considered the bodies thermostat?

A

Hypothalamus

51
Q

What detects a change in skin temperature?

A

Peripheral thermoreceptors in skin?

52
Q

What detects a change in core temperature?

A

Central thermoreceptors in hypothalamus, abdominal organs etc.

53
Q

NB!! What is the response to cold exposure coordinated by?

A

Posterior hypothalamus

54
Q

To increase heat production?

A
  • Increased muscle tone
  • Shivering
  • Increased voluntary exercise(behavioural)
  • Nonshivering thermogenesis
55
Q

To decrease heat loss

A
  • Skin vasoconstriction
  • Postural changes to reduce exposed surface area (behavioural)
  • Warm clothing (behavioural)
56
Q

Shivering

A
  • Un co-ordinated contraction of skeletal muscle (10-20/sec)
  • Fast response
  • Little work
  • Much heat (2-5 fold increase in internal heat production in minutes)
57
Q

Shivering pathway

A 
Inputs
• Central thermoreceptors (tc)
– hypothalamus, CNS, and abdominal organs
• Peripheral thermoreceptors
– Skin (tskin)
Integration
• Hypothalamus
– Thermoregulatory Integrating Centre (TRIC)
Effectors
• Motor neurons
• Skeletal muscle
58
Q

Where does non-shivering thermogenesis occur?

A

Brown adipose tissue (BAT)

59
Q

BAT non-shivering thermogenesis involves…

A

‘Uncoupling’ of mitochondrial oxidative phosphorylation to generate heat

60
Q

What is non-shivering thermogenesis mediated by?

A

– Thyroid hormones
– Sympathetic nervous system
• Adrenaline
(Both of which increase fat metabolism)

61
Q

Important of non-shivering thermogenesis in who?

A

-Newborns

and hibernation?

62
Q

What is the response to heat exposure coordinated by?

A

Anterior hypothalamus

63
Q

To decrease heat production

A
  • Decreased muscle tone

- Decreased voluntary exercise (behavioural)

64
Q

To increase heat loss

A
  • Skin vasodilation
  • Sweating
  • Cool clothing (behavioural)
65
Q

Hyperthermia in sustained exercise

A
  1. At the onset of exercise, the rate of heat production initially exceeds the rate of heat loss so the core temperature rises.
  2. When heat loss mechanisms are reflexly increased sufficiently to equalise the elevated heat production the core temperature stabilised slightly above the resting point for the duration of the exercise.
66
Q

Vasodilation x3

A
  • Skin is an insulator
  • Skin blood flow plays a key role in temperature regulation
  • Capillary loops close to surface of skin
67
Q

Skin blood flow plays a key role in

temperature regulation

A
  • 20-30 times more blood flows through the skin than is needed for skin nutrition
  • In the process of thermoregulation skin blood flow can increase 6-fold
  • The more blood that reaches the skin from the warm
    core, the closer the skin temperature is to Ct.
  • Blood vessels diminish the skin’s effectiveness as an insulator by carrying heat to the surface where it can be lost.
68
Q

Capillary loops close to surface of skin

A
  • Skin arteriolar vasodilatation

- Skin arteriolar vasoconstriction

69
Q

Skin arteriolar vasodilatation

A

Increases flow of heated blood through the skin and promotes heat loss

70
Q

Skin arteriolar vasoconstriction

A

Reduces blood flow through the skin and decreases heat loss by keeping warm blood in the central core - Vasoconstriction caused by sympathetic stimulation which is under hypothalamic control…

71
Q

What is sweating stimulated by?

A

Sympathetic nervous system

– ‘stress’

72
Q

What controls sweating

A

Hypothalamus

73
Q

What is involves in the thermoneutral zone?

A
  • Ambient temperature (ta) 20-30ºC

– Skin vasomotor effects sufficient to control heat loss

74
Q

Ambient temperature <20ºC

A

– Metabolism

– Shivering

75
Q

Ambient temperature >30ºC

A

Sweating is dominant factor

76
Q

Heat loss in sweating

A

By evaporation

77
Q

Max sweating rate

A

<2 litres/hour

78
Q

ta (v small a) =

A

Ambient temperature

79
Q

Hyperthermia defn

A

Temperature above normal range

80
Q

Causes of hyperthermia

A
  • Exercise-induced

* Pathological

81
Q

Fever

A

Elevated body temperature – infection or inflammation

82
Q

What happens to hypothalamic thermostat at higher temperature? and how?

A

‘reset’ – by pyrogens released from leucocytes.

83
Q

Heat exhaustion symtoms

A
  • Excessive sweating
  • Reduced blood volume
  • Impaired blood flow
  • BP falls - Weak/dizzy, Collapse
84
Q

Treatment for heat exhaustion

A 
• Remove from hot
environment
• Replace fluid (cool)
– Infuse?
• Rest
85
Q

Heat stroke temp

A

41ºC or higher

86
Q

Heat stroke description

A
  • Core temp (tc) rises

* CNS malfunction

87
Q

CNS malfunction in heat stroke

A
  • Delirium
  • Unconsciousness
  • Thermoregulatory centre fails
    • Sweating stops…
    • Metabolic rate up
88
Q

Treatment for heat stroke

A 
Reduce tc
- Remove from heat
- Cool the person
• Lavage with tepid water
• Ice pack
• Fan to promote sweating
and evaporation
89
Q

Other name for fever

A

Pyrexia

90
Q

NB!!Mechanism of pyrexia

A

• Innate immune cells such as macrophages encounter bacteria or other pathogens
• Macrophages release endogenous pyrogens (EP)
– e.g. Interleukin-1b
• EP cause prostaglandin (PG) synthesis
• Act on hypothalamic thermosensitive cells
• Set-point ‘re-set’ to 38.9ºC
• Hence 37.8ºC is ‘too cold’
• Activates thermogenesis
– Shivering
• Reduces heat loss
– Vasoconstriction

91
Q

What does aspirin and paracetamol block?

A

Prostaglandin synthesis

92
Q

Hyperpyrexia defn

A

Fever with extreme elevation of body temperature (41.5oC or above)

93
Q

Malignant hyperthermia

A

Drastic and uncontrolled increase in skeletal muscle oxidative metabolism, which overwhelms the body’s capacity to regulate body temperature.

94
Q

Physical occurrence in malignant hyperthermia

A

– Muscle contraction (rigor)
– Acidosis
– Can lead to organ failure and death

95
Q

Cause of malignant hyperthermia

A
  • Adverse reaction to halothane and other gaseous anaesthetics
  • Failure of muscle SR Ca2+ reuptake
96
Q

Treatment for malignant hyperthermia

A
  • Dantrolene is a muscle relaxant that works to reinstate Ca2+ uptake to SR
  • Cooling
  • Treat acidosis
97
Q

Mild hypothermia degrees and symptoms

A

32ºC - Shivering, conscious

98
Q

Moderate hypothermia degrees and symptoms

A

25ºC - impaired motor skills

99
Q

Severe hypothermia degrees and symptoms

A

<25ºC - No shivering, impaired

consciousness/motor skills

Physiology (28 decks)

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