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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
Q

Conduction equation

A

Heat = (Surface Area)(Constant)(Difference between skin and ambient temperature)

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26
Q

Kc (Conductivity Constant) of air and water?

So what?

A

Air - 6 Kcal/hr/m2/1C
Water - 150 kcal/hr/m2/1C

Body is much more vulnerable to temperature change from water

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27
Q

Why do people curl up when they’re cold

A

Decreasing conductive surface

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28
Q

What is convection?

A

Bulk movement of conductive fluid as a function of temperature difference.

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29
Q

How does convection tend to hammen in humans?

A

Replacement of warm air near the skin with cooler ambient temperature air

Typically leads to cooling (like with an electric fan)

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30
Q

What emits radiation? Who absorbs radiation?

A

Everything above absolute zero.

Also…basically everything.

31
Q

Equation for Heat associated with radiation.

A

Heat = (Surface Area Exposed)(Radiative Char of Medium)(Difference between Skin Temp and Radiant environment temp)

32
Q

In a comfortable, indoor room, what is the distribution of heat loss causes?

A

85% via conduction/convection + Radiation

15% via insensible evaporation

33
Q

Which heating routes are bidirectional? Unidirectional?

A

Bidirectional – Radiative, Conductive/Convective

Uni – Evaporative

34
Q

In temperatures above 35C (95F), what is the distribution of heat loss causes?

A

Basically all via evaporation

35
Q

Influence of humidity on heat control?

A

Very humid air can’t hold the moisture required to evap. sweat

36
Q

What does Core Temperature describe?

A

Rlatively Uniform temperature distribution throughout the body trunk

37
Q

Best measure of core temp? Three acceptable substitutes?

A

Pulmonary Artery Catheter

Oral, Rectal, Tympanic

38
Q

Relationship of capillary beds and heat control?

A

Conduction between capillary blood (Tc) and Skin surface (Tskin)

39
Q

In hyperthermia, how will the body modify bloodflow? Why?

A

Decrease Tskin relative to Tambient to enhance heat loss

Also decreases blood flow to the core

40
Q

Two types of temperature receptors

A

Cutaneous and Core

41
Q

Where are core thermoreceptors?

A

Pre-optic area of the hypothalamus

Spinal Cord

42
Q

Three major thermoregulatory states?

A

Vasomotor Regulation
Metabolic Regulation
Combined sudomotor and vasomotor

43
Q

When does vasomotor regulation occur? What does it entail?

A

Mild levels of thermal stress or exercise.

Changes skin blood flow

44
Q

When does Metabolic regulation occur? What does it entail?

A

When maximal vasoconstriction is ineffective

Voluntary Exercise, Shivering

45
Q

Why is shivering an ineffective heating mechanism.

A

While it increases heat production, it increases conductive and convective heat loss.

46
Q

When does combined-sudomotor/vasomotor regulation occur? What does it entail?

A

In response to heat accumulation

Elevation of BT causes increases in sweat and vasodil.

47
Q

He kept describing the hypothalamus as a…

A

thermostat

48
Q

Describe the natural circadian rhythm of temperature.

A

Coldest pre-dawn

Highest in early evening

49
Q

What are pyrogens?

A

Chemicals that cause a febrile response.

50
Q

Source of exogenous pyrogens

A

heat-stable, high MW polysaccharides from G- bac

51
Q

Where do endogenous pyrogens come from.

A

Heat-labile proteins from monos, macros, and kupffers in resp. to bacteria

52
Q

The most important endogenous pyrogen?

A

Interleukin 1beta

53
Q

What does Il-1beta do?

A

Produces fever through direct action on the Hypothal.
Immune system activation
Neutrophil release
Increased Ab production

54
Q

Action of Il-1beta MAY be associated with what signalling molecule?

A

Prostaglandin E2

55
Q

2nd place pyrogen? Its origin?

A

TNF- macrophages exposed to gram negatives

56
Q

Typical cause of hyperthermia?

A

Applied heat-load from over exertion, high ambient temperature, or both.

57
Q

Three broad causes of hyperthermia

A

Excessive Heat Production
Diminished Heat Dissipation
Hypothalamic Dysfunction

58
Q

Example causes of excessive heat production

A

Delirium tremens
Malignant hyperthermia of anastesis
Thyrotoxicosis

59
Q

Example causes of diminished heat dissipation?

A

Anticholinergic drugs
Dehydration
Occlusive Dressings

60
Q

Example causes of hypothalamic dysfunction

A

Stroke
Infection
Trauma
Tumor

61
Q

Autonomic response to hyperthermia?

A

Increase in subcutaneous bloodflow (if desperate, up to 60% of total CO)

62
Q

Difference in autonomic effects in apical and non-apical regions?

A

Apical – Inhibition of tonic vasoconstriction

Non-apical – active vasodilation

63
Q

Two types of heatstroke?

A

Classical, Exertional

64
Q

Common cause of classical heatstroke?

A

Excessive heat and humidity

Fluid loss from sweating -> dehydration -> more heat

65
Q

Role of BP in heatstroke?

A

Decreased subcu. resistance -> BP Drop

Loss of water sweating -> BP Drop

66
Q

What causes exertional hyperthermia?

A

Voluntary muscular activity coupled with environmental heat stress.

67
Q

How does exercise make heatstroke worse?

A

Muscle generates increased heat directly and through increased CO
Exercise induces peripheral vasoconstriction (this is eventually overridden)

68
Q

Effect of vasodilation at the periphery and in the skeletal muscles at the same time + sweating?

A

Huge BP drop

69
Q

How to manage heatstroke?

A

Physical methods (cool bath, fanning)

70
Q

Difference in response to pathological vs environmental overheating

A

Pathogens – Anti-pyretics

Env. – Physical methods

71
Q

How cold is hypothermia?

A

Below approx. 92F

72
Q

When is clinical hypothermia applied?

A

In surgery to reduce O2 requirements and BP

73
Q

Why to watch patients under or recently under sedation?

A

Suppression of hypothalamus

Physiology - Pulmonary (5 decks)

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