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Physiology 1 > Lecture 3 thermoregulation > Flashcards

Lecture 3 thermoregulation Flashcards

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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
Why control temperature?
Metabolic rate is very temperature sensitive
26
At what high temperature does death occur?
42.5 degrees C
27
What happens to the body at lower temperatures?
Loss of consciousness, decrease in HR/arrhythmia's, death (27.5 degrees)
28
What is the name given to maintenance of the core temperature?
Thermoregulation
29
What is core body temperature?
Temperature of the body around the main organs
30
Where is the core body temp 37.8 degrees C?
CNS, abdominal and thoracic cavities
31
Where is the shell temp found?
Skin and subcutaneous fat
32
What temperatures does the shell temp fluctuate between?
20 and 40 degrees C
33
How is heat exchanged between the core and the shell?
Via blood
34
Why is thermoregulation important for cellular function?
Ensures optimal temp for cellular metabolism
35
When does body temperature change?
``` Diurnal variation Menstrual cycle Exercise Age Ambient temperature ```
36
What happnes to body temperature after ovulation?
Increases
37
Advantages and disadvantages of oral measurement of core temperature.
- Simple, non-invasive | - Can underestimate Tc
38
Advantages and disadvantages of Aural measurment of core temp?
- Fast | - Can be uncomfortable, can underestimate Tc
39
Advantages and disadvantages of rectal measurement of core temperature.
- Continuous, close to Tc | - Slow
40
Advantages and disadvantages of oesophageal measurement of Tc
- Continuous, close to Tc | - Slow, affected by food and drink
41
Advantages and disadvantages of GI tract measurement of core temp.
- Temperature pill radio transmitter continuous | - Varies along track, has to be retrieved
42
What are the 4 mechanisms of heat transfer?
Radiation, convection, conduction, evaporation
43
What % of heat transfer does evaporation account for?
22%
44
What % of heat transfer does radiation account for?
60%
45
What % of heat transfer does conduction to the air account for?
15%
46
Give an example of convection.
Air currents
47
What mechanism of heat transfer accounts for 3% of heat transfer?
Conduction to objects
48
What is radiation as a mechanism of heat transfer?
Emission of heat energy from surface of warm body via electromagnetic waves
49
What is convection?
A gravitationally-induced heat transport, driven by the expansion of air or fluid containing heat
50
What are convection currents?
Warm air rises and is replaced by cool air
51
Give two examples of convection as a mechanism of heat transfer.
Air currents | Water currents
52
Why is little heat lost by conduction under normal conditions?
Still air (in clothing) is a poor conductor
53
What is the thermal conductivity of water compared to air?
25 x
54
Define conduction
Transfer of heat between objects in direct contact
55
In what way does water evaporate from the skin and lungs?
Insensibly
56
What does it mean that water evaporates insensibly from the skin and lungs?
The heat loss cannot be controlled for purposes of temperature regulation (passive)
57
How much energy is there in the evaporation of 1L of water?
2,400KJ
58
What is the daily insensible water loss?
800ml, around 20 Watt
59
How does sweat cool things down
Requires thermal energy, absorbed from the skin which cools the body
60
What is sensible loss of heat/
Regulated by sympathetic nervous control (sweating from eccrine sweat glands)
61
How much water is loss through sensible loss on a normal day?
100ml
62
How much water is lost through sensible loss in a hot environment in a day?
1.5L
63
How much water is lost through sensible loss during vigorous exercise per day?
4L
64
What are the possible heat inputs?
Oxidation of fuel | Environment
65
What is the efficiency of heat input from oxidation of fuel?
50%
66
What centers are involved in the negative feedback reflex arcs in the autonomic nervous system?
Neuronal integrating centers
67
Where are neuronal integrating centers found?
Midbrain and brain-stem
68
What parts of the brain make up the neuronal intergrating centers within the midbrain and brain-stem?
Hypothalamus, pons, medulla
69
Name 4 things under the control of the autonomic nervous system.
Temperature control Osmolarity control Blood pressure/flow control Blood gas/ventilation control
70
What is the hypothalamus?
Thermoregulatory integrating centre of central and peripheral sensory information
71
What region of the hypothalamus is activated by the cold?
Posterior region
72
What region of the hypothalamus is activated by the heat/
Anterior region
73
What size changes does the hypothalamus respond to?
0.01 degrees C
74
What is the centre of thermoregulation?
No one area, a heirachy extends through hypothalamus, brainstem and spinal cord
75
What parts of the nervous system provide higher control of thermoregulation?
Medial and lateral parts of preoptic nucleus, anterior hypothalamus and nearby regions of septum (preoptic region)
76
What parts of the nervous system crudely sense changes in Tc and initiate certain responses?
Lower brain stem and spinal structures
77
What are the three types of effectors involved in thermoregulation?
Peripheral blood vessels, sweat glands (eccrine), skeletal muscles
78
What are the two types of receptors involved in thermoregulation?
Peripheral thermoreceptors in skin | Central thermoreceptors in hypothalamus, abdominal organs and elsewhere
79
How do peripheral blood vessels act as effectors during thermoregulation?
Vasoconstriction/dilation alters blood flow to the skin
80
How does vasoconstriction/dilations change body temperature?
Controls conductive and radiative heat loss
81
What is another mechanism by which blood vessles can control blood temperature?
Countercurrent exchange mechanism
82
How are the blood vessles involved in the countercurrent exchange mechanism arranged?
Arteries transport warm blood, deep veins positioned alongside arteries
83
What happens in the cold with respect to the countercurrent exchange mechanism
Blood returns through deep veins, heat transfers from arteries to veins which conserves heat
84
What happens when heat wants to be lost with respect to the countercurrent exchange system?
Deep veins vasoconstrict, more blood flows through superficial veins
85
How do sweat glands act as effectors during thermoregulation?
Control evaporative heat loss
86
How do skeletal muscles bring about thermoregulation?
Shivering- rapid involuntary rhythmic contractions (10-20/sec) liberated energy converted to heat
87
What increase in heat can shivering cause?
2-5 fold increase in heat within seconds/minutes
88
What can inhibit shivering?
Heat signals from preoptic region
89
How do babies produce heat?
Non-shivering thermogenesis via brown adipose tissue
90
How does brown fat generate heat
Oxidative phosphorylation in the mitochondria is uncoupled
91
How is temperature gradient between skin and environment altered?
Radius of blood vessles determine blood flow
92
By what amount does skin blood flow vary?
400-2500ml/min
93
An increase in sympathetic activity leads to what vasomotor response?
Vasoconstriction
94
What part of the brain is responsible for behavioural heat production/conservation?
Hypothalamus and limbic system
95
What part of the nervous sytem is responsible for piloerection?
Sympathetic NS
96
How does piloerection decrease thermal gradient?
Muscles at base of hair contract, creating dead space
97
Define fever.
Elevation of body temperature as a result of infection/inflammation (trigger)
98
What is the response to a fever trigger?
White blood cells proliferate and secrete chemical substances
99
What 'fever-inducers' do white blood cells secrete in response to triggers?
Endogenous pyrogens
100
What do endogenous pyrogens do?
Stimulate release of prostoglandins
101
What do prostoglandins do?
Increase the hypothalamic set point

Physiology 1 (9 decks)

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