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Physiology 1 > Lecture 3 thermoregulation > Flashcards

Lecture 3 thermoregulation Flashcards

1
Q

Define homeostasis.

A

The dynamic maintenance of physiological variables within a predictable range

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2
Q

What does dynamic mean, within the context of homeostasis?

A

The variable fluctuates within a normal range, and the average value is predictable over longer periods of time

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3
Q

What is the short term purpose of homeostasis?

A

Immediate survival

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4
Q

What is the medium to long term purpose of homeostasis?

A

Health and well-being

Reproductive capability

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5
Q

What does homeostatic control mechanisms ensure?

A

Changes in physiological variables are normalised

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6
Q

Negative feedback is also known as?

A

Reflex arcs

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7
Q

Describe negative feedback.

A

Change in regulated variable compared against set point, response moves variable back to set point (normalisation)

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8
Q

When may set points need to be changed or over-ridden?

A

When physiological circumstances change (fever, exercise)

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9
Q

What are the three types of negative feedback?

A

Neuronal
Endocrine
Local (chemical/physical)

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10
Q

What is feed-forward?

A

Anticipation of a change brings about response to change before detected by negative feedback sensors

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11
Q

What is positive feedback?

A

Change in variable triggers response that causes further change to variable (amplification)

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12
Q

How much ATP does the heart consume per day?

A

6KG

20-30x it’s own weight

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13
Q

How many times does the heart beat per day?

A

100,000

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14
Q

How much blood does the heart beat per day?

A

10 tons

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15
Q

What physiological variables are required for immediate survival?

A

Oxygen and glucose supply to all cells (more immediate importance to brain)

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16
Q

What physiological variables are responsible for optimal functioning of organs and tissues?

A

Temperature, metabolic rate

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17
Q

What physiological variables are responsible for fulfilling dietary requirements?

A

Appetite

Gastro-intestinal secretions, motility and absorption

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18
Q

What variables are responsible for gene expression?

A

Environmental factors and hormone levels

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19
Q

What physiological variables are responsible for reproductive capability?

A

Hormone level

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20
Q

Control of body temperature is an example of what type of negative feedback reflex arc?

A

Neuronal negative feedback reflex arc

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21
Q

What name is given to organisms whose body temperature varies with environmental temperature?

A

Poikilotherms

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22
Q

What names is given to organisms whose core body temperature is maintained within narrow constant range despite variations in environmental temperature?

A

Homeotherms

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23
Q

What is the heat source for homeotherms?

A

Internal: by-product of metabolism

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24
Q

What is basal metabolic rate?

A

The minimum level of energy required to live, generates heat

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25
Q

Why control temperature?

A

Metabolic rate is very temperature sensitive

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26
Q

At what high temperature does death occur?

A

42.5 degrees C

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27
Q

What happens to the body at lower temperatures?

A

Loss of consciousness, decrease in HR/arrhythmia’s, death (27.5 degrees)

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28
Q

What is the name given to maintenance of the core temperature?

A

Thermoregulation

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29
Q

What is core body temperature?

A

Temperature of the body around the main organs

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30
Q

Where is the core body temp 37.8 degrees C?

A

CNS, abdominal and thoracic cavities

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31
Q

Where is the shell temp found?

A

Skin and subcutaneous fat

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32
Q

What temperatures does the shell temp fluctuate between?

A

20 and 40 degrees C

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33
Q

How is heat exchanged between the core and the shell?

A

Via blood

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34
Q

Why is thermoregulation important for cellular function?

A

Ensures optimal temp for cellular metabolism

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35
Q

When does body temperature change?

A 
Diurnal variation
Menstrual cycle
Exercise
Age
Ambient temperature
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36
Q

What happnes to body temperature after ovulation?

A

Increases

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37
Q

Advantages and disadvantages of oral measurement of core temperature.

A
  • Simple, non-invasive

- Can underestimate Tc

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38
Q

Advantages and disadvantages of Aural measurment of core temp?

A
  • Fast

- Can be uncomfortable, can underestimate Tc

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39
Q

Advantages and disadvantages of rectal measurement of core temperature.

A
  • Continuous, close to Tc

- Slow

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40
Q

Advantages and disadvantages of oesophageal measurement of Tc

A
  • Continuous, close to Tc

- Slow, affected by food and drink

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41
Q

Advantages and disadvantages of GI tract measurement of core temp.

A
  • Temperature pill radio transmitter continuous

- Varies along track, has to be retrieved

42
Q

What are the 4 mechanisms of heat transfer?

A

Radiation, convection, conduction, evaporation

43
Q

What % of heat transfer does evaporation account for?

A

22%

44
Q

What % of heat transfer does radiation account for?

A

60%

45
Q

What % of heat transfer does conduction to the air account for?

A

15%

46
Q

Give an example of convection.

A

Air currents

47
Q

What mechanism of heat transfer accounts for 3% of heat transfer?

A

Conduction to objects

48
Q

What is radiation as a mechanism of heat transfer?

A

Emission of heat energy from surface of warm body via electromagnetic waves

49
Q

What is convection?

A

A gravitationally-induced heat transport, driven by the expansion of air or fluid containing heat

50
Q

What are convection currents?

A

Warm air rises and is replaced by cool air

51
Q

Give two examples of convection as a mechanism of heat transfer.

A

Air currents

Water currents

52
Q

Why is little heat lost by conduction under normal conditions?

A

Still air (in clothing) is a poor conductor

53
Q

What is the thermal conductivity of water compared to air?

A

25 x

54
Q

Define conduction

A

Transfer of heat between objects in direct contact

55
Q

In what way does water evaporate from the skin and lungs?

A

Insensibly

56
Q

What does it mean that water evaporates insensibly from the skin and lungs?

A

The heat loss cannot be controlled for purposes of temperature regulation
(passive)

57
Q

How much energy is there in the evaporation of 1L of water?

A

2,400KJ

58
Q

What is the daily insensible water loss?

A

800ml, around 20 Watt

59
Q

How does sweat cool things down

A

Requires thermal energy, absorbed from the skin which cools the body

60
Q

What is sensible loss of heat/

A

Regulated by sympathetic nervous control (sweating from eccrine sweat glands)

61
Q

How much water is loss through sensible loss on a normal day?

A

100ml

62
Q

How much water is lost through sensible loss in a hot environment in a day?

A

1.5L

63
Q

How much water is lost through sensible loss during vigorous exercise per day?

A

4L

64
Q

What are the possible heat inputs?

A

Oxidation of fuel

Environment

65
Q

What is the efficiency of heat input from oxidation of fuel?

A

50%

66
Q

What centers are involved in the negative feedback reflex arcs in the autonomic nervous system?

A

Neuronal integrating centers

67
Q

Where are neuronal integrating centers found?

A

Midbrain and brain-stem

68
Q

What parts of the brain make up the neuronal intergrating centers within the midbrain and brain-stem?

A

Hypothalamus, pons, medulla

69
Q

Name 4 things under the control of the autonomic nervous system.

A

Temperature control
Osmolarity control
Blood pressure/flow control
Blood gas/ventilation control

70
Q

What is the hypothalamus?

A

Thermoregulatory integrating centre of central and peripheral sensory information

71
Q

What region of the hypothalamus is activated by the cold?

A

Posterior region

72
Q

What region of the hypothalamus is activated by the heat/

A

Anterior region

73
Q

What size changes does the hypothalamus respond to?

A

0.01 degrees C

74
Q

What is the centre of thermoregulation?

A

No one area, a heirachy extends through hypothalamus, brainstem and spinal cord

75
Q

What parts of the nervous system provide higher control of thermoregulation?

A

Medial and lateral parts of preoptic nucleus, anterior hypothalamus and nearby regions of septum (preoptic region)

76
Q

What parts of the nervous system crudely sense changes in Tc and initiate certain responses?

A

Lower brain stem and spinal structures

77
Q

What are the three types of effectors involved in thermoregulation?

A

Peripheral blood vessels, sweat glands (eccrine), skeletal muscles

78
Q

What are the two types of receptors involved in thermoregulation?

A

Peripheral thermoreceptors in skin

Central thermoreceptors in hypothalamus, abdominal organs and elsewhere

79
Q

How do peripheral blood vessels act as effectors during thermoregulation?

A

Vasoconstriction/dilation alters blood flow to the skin

80
Q

How does vasoconstriction/dilations change body temperature?

A

Controls conductive and radiative heat loss

81
Q

What is another mechanism by which blood vessles can control blood temperature?

A

Countercurrent exchange mechanism

82
Q

How are the blood vessles involved in the countercurrent exchange mechanism arranged?

A

Arteries transport warm blood, deep veins positioned alongside arteries

83
Q

What happens in the cold with respect to the countercurrent exchange mechanism

A

Blood returns through deep veins, heat transfers from arteries to veins which conserves heat

84
Q

What happens when heat wants to be lost with respect to the countercurrent exchange system?

A

Deep veins vasoconstrict, more blood flows through superficial veins

85
Q

How do sweat glands act as effectors during thermoregulation?

A

Control evaporative heat loss

86
Q

How do skeletal muscles bring about thermoregulation?

A

Shivering- rapid involuntary rhythmic contractions (10-20/sec) liberated energy converted to heat

87
Q

What increase in heat can shivering cause?

A

2-5 fold increase in heat within seconds/minutes

88
Q

What can inhibit shivering?

A

Heat signals from preoptic region

89
Q

How do babies produce heat?

A

Non-shivering thermogenesis via brown adipose tissue

90
Q

How does brown fat generate heat

A

Oxidative phosphorylation in the mitochondria is uncoupled

91
Q

How is temperature gradient between skin and environment altered?

A

Radius of blood vessles determine blood flow

92
Q

By what amount does skin blood flow vary?

A

400-2500ml/min

93
Q

An increase in sympathetic activity leads to what vasomotor response?

A

Vasoconstriction

94
Q

What part of the brain is responsible for behavioural heat production/conservation?

A

Hypothalamus and limbic system

95
Q

What part of the nervous sytem is responsible for piloerection?

A

Sympathetic NS

96
Q

How does piloerection decrease thermal gradient?

A

Muscles at base of hair contract, creating dead space

97
Q

Define fever.

A

Elevation of body temperature as a result of infection/inflammation (trigger)

98
Q

What is the response to a fever trigger?

A

White blood cells proliferate and secrete chemical substances

99
Q

What ‘fever-inducers’ do white blood cells secrete in response to triggers?

A

Endogenous pyrogens

100
Q

What do endogenous pyrogens do?

A

Stimulate release of prostoglandins

101
Q

What do prostoglandins do?

A

Increase the hypothalamic set point

Physiology 1 (9 decks)

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