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Physiology - Pulmonary > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

Heat is produced largely by…

A

Oxidative Metabolism

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2
Q

Primary molecular source of body heat?

A

Glucose

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3
Q

What is a Calorie?

A

Energy to raise 1 gram of water from 0 to 1C

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4
Q

Heat generated by combustion of glucose?

A

686 kCal/mol

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5
Q

Energy released from oxidative metabolism of glucose?

A

420 kCal/mole Heat

266 kCal/mole ATP high energy bonds

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6
Q

Does tissue mass correlate with heat generation?

A

No. Kidneys/Heart/Lungs/Brain are 7.7% of body mass but generate 72.4% of body heat.

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7
Q

Human heat production at rest?

A

1Kcal/hour/kg

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8
Q

If heat loss didn’t exist, a person would heat up at

A

More than 1Cel. per hour without exercise

more than 10X that with exercise

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9
Q

Difference between oral and rectal temperature values?

A

Rectal tend to be about a degree higher

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10
Q

Temperature increases of how much can be damaging?

A

4-5C (7-9 F)

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11
Q

Problem with lowered temperature?

A

Impairment and eventual loss of Temperature Regulation

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12
Q

Name three physical factors governing temperature control.

A

Evaporation
Conduction/Convection
Radiation

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13
Q

Two types of evaporation?

A

Insensible Evaporation

Sensible Evaporation

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14
Q

How much energy is required for evaporation?

A

584 cal/gram

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15
Q

Two sources of insensible evaporation?

A

Saturation of Expired Air

Diffusive Loss from epidermis via stratum conium

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16
Q

Total loss from insensible evaporation (volume and heat)

A

1 liter/day

584 Kcal

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17
Q

What percentage of normal caloric intake is used on hear loss?

A

25%

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18
Q

What situations might cause water loss problems use to insensible evaporation?

A

High Altitudes (increased ventilation)
Loss of Strat. Conium in burns
Exposure of wet tissue in surgery

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19
Q

What is sensible evaporation

A

Sweating

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20
Q

Cause of sweating?

A

Cholinergic sympathetic stimulation of sweat glands

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21
Q

How fast is fluid lost sweating?

A

Up to 2 liters/hour

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22
Q

What is sweat…really?

Why do we care?

A

A dilute salt solution.
Mostly NaCl, some KCl, urea, Organic Acid

Heavy sweating cause major water AND salt loss

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23
Q

Describe an environment in which sweating will not be a useful process?

A

Air temperature > Skin temp

Air is saturated

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24
Q

What is conduction?

A

Change of temperature caused by contact of the body with other conductive fluids (air/water)

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25
Conduction equation
Heat = (Surface Area)(Constant)(Difference between skin and ambient temperature)
26
Kc (Conductivity Constant) of air and water? So what?
Air - 6 Kcal/hr/m2/1C Water - 150 kcal/hr/m2/1C Body is much more vulnerable to temperature change from water
27
Why do people curl up when they're cold
Decreasing conductive surface
28
What is convection?
Bulk movement of conductive fluid as a function of temperature difference.
29
How does convection tend to hammen in humans?
Replacement of warm air near the skin with cooler ambient temperature air Typically leads to cooling (like with an electric fan)
30
What emits radiation? Who absorbs radiation?
Everything above absolute zero. | Also...basically everything.
31
Equation for Heat associated with radiation.
Heat = (Surface Area Exposed)(Radiative Char of Medium)(Difference between Skin Temp and Radiant environment temp)
32
In a comfortable, indoor room, what is the distribution of heat loss causes?
85% via conduction/convection + Radiation | 15% via insensible evaporation
33
Which heating routes are bidirectional? Unidirectional?
Bidirectional -- Radiative, Conductive/Convective | Uni -- Evaporative
34
In temperatures above 35C (95F), what is the distribution of heat loss causes?
Basically all via evaporation
35
Influence of humidity on heat control?
Very humid air can't hold the moisture required to evap. sweat
36
What does Core Temperature describe?
Rlatively Uniform temperature distribution throughout the body trunk
37
Best measure of core temp? Three acceptable substitutes?
Pulmonary Artery Catheter | Oral, Rectal, Tympanic
38
Relationship of capillary beds and heat control?
Conduction between capillary blood (Tc) and Skin surface (Tskin)
39
In hyperthermia, how will the body modify bloodflow? Why?
Decrease Tskin relative to Tambient to enhance heat loss | Also decreases blood flow to the core
40
Two types of temperature receptors
Cutaneous and Core
41
Where are core thermoreceptors?
Pre-optic area of the hypothalamus | Spinal Cord
42
Three major thermoregulatory states?
Vasomotor Regulation Metabolic Regulation Combined sudomotor and vasomotor
43
When does vasomotor regulation occur? What does it entail?
Mild levels of thermal stress or exercise. | Changes skin blood flow
44
When does Metabolic regulation occur? What does it entail?
When maximal vasoconstriction is ineffective | Voluntary Exercise, Shivering
45
Why is shivering an ineffective heating mechanism.
While it increases heat production, it increases conductive and convective heat loss.
46
When does combined-sudomotor/vasomotor regulation occur? What does it entail?
In response to heat accumulation | Elevation of BT causes increases in sweat and vasodil.
47
He kept describing the hypothalamus as a...
thermostat
48
Describe the natural circadian rhythm of temperature.
Coldest pre-dawn | Highest in early evening
49
What are pyrogens?
Chemicals that cause a febrile response.
50
Source of exogenous pyrogens
heat-stable, high MW polysaccharides from G- bac
51
Where do endogenous pyrogens come from.
Heat-labile proteins from monos, macros, and kupffers in resp. to bacteria
52
The most important endogenous pyrogen?
Interleukin 1beta
53
What does Il-1beta do?
Produces fever through direct action on the Hypothal. Immune system activation Neutrophil release Increased Ab production
54
Action of Il-1beta MAY be associated with what signalling molecule?
Prostaglandin E2
55
2nd place pyrogen? Its origin?
TNF- macrophages exposed to gram negatives
56
Typical cause of hyperthermia?
Applied heat-load from over exertion, high ambient temperature, or both.
57
Three broad causes of hyperthermia
Excessive Heat Production Diminished Heat Dissipation Hypothalamic Dysfunction
58
Example causes of excessive heat production
Delirium tremens Malignant hyperthermia of anastesis Thyrotoxicosis
59
Example causes of diminished heat dissipation?
Anticholinergic drugs Dehydration Occlusive Dressings
60
Example causes of hypothalamic dysfunction
Stroke Infection Trauma Tumor
61
Autonomic response to hyperthermia?
Increase in subcutaneous bloodflow (if desperate, up to 60% of total CO)
62
Difference in autonomic effects in apical and non-apical regions?
Apical -- Inhibition of tonic vasoconstriction | Non-apical -- active vasodilation
63
Two types of heatstroke?
Classical, Exertional
64
Common cause of classical heatstroke?
Excessive heat and humidity | Fluid loss from sweating -> dehydration -> more heat
65
Role of BP in heatstroke?
Decreased subcu. resistance -> BP Drop | Loss of water sweating -> BP Drop
66
What causes exertional hyperthermia?
Voluntary muscular activity coupled with environmental heat stress.
67
How does exercise make heatstroke worse?
Muscle generates increased heat directly and through increased CO Exercise induces peripheral vasoconstriction (this is eventually overridden)
68
Effect of vasodilation at the periphery and in the skeletal muscles at the same time + sweating?
Huge BP drop
69
How to manage heatstroke?
Physical methods (cool bath, fanning)
70
Difference in response to pathological vs environmental overheating
Pathogens -- Anti-pyretics | Env. -- Physical methods
71
How cold is hypothermia?
Below approx. 92F
72
When is clinical hypothermia applied?
In surgery to reduce O2 requirements and BP
73
Why to watch patients under or recently under sedation?
Suppression of hypothalamus

Physiology - Pulmonary (5 decks)

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