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Physiology Pulmonary > thermoregulation > Flashcards

thermoregulation Flashcards

1
Q

what re heat sources?

A

combustion of glucose (680Kcal.mole as heat), oxidative metabolism of glucose (420 Kcal/mole as heat, 266 Kcal/mole as ATP high energy bonds)

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2
Q

what is the human heat production at rest?

A

1 Kcal/hour/Kg

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3
Q

what temperature increase is potentially lethal?

A

increase of greater than 4-5 degrees C. (7-9 degrees F)

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4
Q

what energy is required for evaporation of water (liquid) to gas phase?

A

584 Kcal/mole

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5
Q

what are the 2 sources of insensible evaporation?

A

loss due to saturation of expired air and diffusive loss from epidermis via the stratum conium.

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6
Q

what are sensible evaporation?

A

sweating due to sympathetic stimulation

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7
Q

what is conduction?

A

heat can be lost or gained by contact of body with other conductive fluids, namely water or air (equation in notes).

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8
Q

when is sweat not removing heat?

A

when the air temperature is less than the skin temperature and air is saturation, sweat will not evaporate and just drip off.

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9
Q

equation for conduction?

A

Heat= AcKc(Tskin-Tambient)

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10
Q

what are some physiological thermoregulatory compensation?

A

putting on more clothes, but generally involves changing temperature of the skin

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11
Q

why is danger of hypothermia greater in water than air?

A

K value for water is 25 times greater than for air

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12
Q

what is convection?

A

bulk movement of conductive fluid as a function of temperature differences within the fluid.

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13
Q

what is a way to enhance conductive heat loss?

A

replacing warm air near the skin with cooler ambient temperature air (with a fan)

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14
Q

why does curling up when cold help?

A

reduces Ac (surface area)

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15
Q

what does the body do when exposed to radiation?

A

absorbs radiant energy, and int he case of a cold environment-> body may become source of radiant energy

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16
Q

equation for radiation?

A

heat=ArKr(Tskin-Tradiator)

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17
Q

what are the relative percentages of heat loss?

A

in an indoor room: 85% of heat loss is via conduction/convection and radiation, remaining 15% due to insensible evaporation.

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18
Q

what is the 85% is equally divided between?

A

conduction and radiation due to nearly equal Ac and Ar, and Kc and Kr values, and equilibrium of air radiant surface temperatures.

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19
Q

what is the difference physiological heat loss and evaporative heat transfer?

A

radiative and conductive/convective heat routes are bi-directional, while evaporative heat transfer always results in heat loss.

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20
Q

as ambient temperature raises, what happens to the proportion of heat loss?

A

as ambient temperature raises the proportion of heat loss via evaporation increases dramatically.

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21
Q

where can the body temperature be taken from?

A

oral, rectal, pulmonary artery catheter (best), and tympanic membrane.

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22
Q

what is heat exchange dominated by?

A

conduction between capillary blood and the normally cooler skin surface.

23
Q

what happens during hypothermia?

A

vasoconstriction to reduce blood flow near skin, lower T skin relative to T ambient thus reducing further heat loss.

24
Q

what happens during hyperthermia?

A

vasodilation of blood vessels, body increases T skin relative to T ambient to enhance heat loss-> this decreases blood flow to core (and CNS). Especially important factor in infants where ratio of body surface area to weight is greater than in adults

25
Q

how does the skin respond to temperature changes?

A

cutaneous thermoreceptors, certain neurons distributed over the skin surface can respond to either heating (warming receptors) or cooling (cold) receptors

26
Q

how does our core respond to temperature changes?

A

neurons in pre-optic area of hypothalamus and spinal cord which respond to direct heating and cooling of these areas.

27
Q

what are the 3 major thermoregulatory states that all serve to maintain the core?

A

Vasomotor regulation, metabolic regulation, and combined sudomotor and vasomotor regulation

28
Q

which thermoregulator represents the normal resting state?

A

vasomotor regulation: mild levels of thermal stress or exercise, changes in skin blood flow are sufficient to regulate temperature

29
Q

which thermoregulator starts when maximal vasoconstriction is ineffective in preventing heat loss?

A

metabolic regulation->response include: voluntary exercise and shivering

30
Q

why does shivering occur?

A

when Tc drops below a certain threshold, limited effectiveness in elevating temperature because it increases conductive and convection loss by increasing blood flow from core to muscles by increasing movement of body

31
Q

which thermoregulator is in response to heat accumulation?

A

combine sudomotor and vasomotor regulation. Elevation in body temperature causes progressive increases in sweating and active metabolism

32
Q

For the natural circadian rhythm in body temperature, when is the lowest and peak of body temperatures?

A

Early evening-> highest

Pre-dawn-> lowest

33
Q

during a fever, what center is involved in the temperature increase?

A

hypothalamus temperature is set point, is increased to a new higher temperature and body temperature is elevated above normal

34
Q

what are pyrogen?

A

chemicals that cause a febrile response.

35
Q

What are two examples of pyrogens?

A

exogenous: heat-stable, high MW polysacc. product from G(-) bacteria
endogenous: heat-LIABLE proteins released by monocytes, macrophages, and kupffer cells in response to bacterial pyrogens

36
Q

most important endogenous factor?

A

interleukin 1 beta

37
Q

how does interleukin 1 beta cause a fever?

A

by direct action on the hypothalamus

38
Q

what is another important cytokine/pyrogen?

A

TNF, produced by macrophages in response to G(-) bacterial endotoxin

39
Q

why might IL-1 beta work via prostoglandin E2?

A

injection of PGE2 into hypothalamus is pyrogenic and addition of aspirin inhibits PGE2 synthesis

40
Q

hyperthermia (heatstroke) is due to?

A

exogenously applied heat-load from over exertion, high ambient temperatures or both

41
Q

what sore some causes of excessive heat production?

A

delirium tremens, drug abuse, exertional hyperthermia, lethal catatonis, generalized tetanus

42
Q

what are some things that could cause diminished heat dissipation?

A

anti-cholinergic drugs, autonomic dysfunction, dehydration, heatstroke, neuroleptic malignant syndrome

43
Q

what are some disorders that can cause hypothalamic dysfunction?

A

cerebrovascular accidents, encephalitis, trauma, tumors, neuroleptic malignant syndrome

44
Q

what is the overall response to hyperthermia?

A

increase in subcutaneous blood flow to increase heat loss

45
Q

what is the normal conditions of subcutaneous blood flow?

A

300-500 ml/minute, 5-10% Cardiac output

46
Q

what can heat stress do to the normal subcutaneous blood flow?

A

increase it
cardiac output can rise from 6 liters to 13 liters
blow flow to skin can increase to 8 liters (60% CO)

47
Q

in hyperthermia, was is the response to apical regions? (hands, feet, etc)

A

primarily inhibit tonically expressed vasoconstriction

48
Q

in hyperthermia, was is the response to non-apical regions?

A

small increase in flow, due to removal of vasoconstriction, but the major factor increasing blood flow is active vasodilation

49
Q

what is the classical heatstroke characterized by?

A

due to excessive heat or humidity, causing increased body temperature with poor heat dissipation due to ineffectiveness of evaporative cooling.

50
Q

what are some complicating factors of hyperthermia?

A

dehydration, and drop in blood pressure due to decreased subcutaneous resistance-> replace fluid WITH electrolytes

51
Q

what is exertional hyperthermia?

A

due to voluntary muscular activity coupled with environmental heat stress (heavy exercising in hot or humid climates). Combined effect of vasodilation, demand for increased blood flow to skeletal muscle and fluid loss by sweating can cause sudden drop in blood pressure

52
Q

how is management hyperthermia treated?

A

physical cooling, anti-pyretics not useful

53
Q

why is hypothermia potentially dangerous?

A

if the core temperature drops below 90 degrees f, then hypothalamic compensatory mechanism fail

54
Q

when is clinical hypothermia use?

A

in surgical procedures to reduce O2 requirements and blood pressure/bleeding. With ventilation and cardiac assistance, core temperature ca be maintained at 70-75 degrees F for many hours.

Physiology Pulmonary (4 decks)

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