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medical physiology > Chapter 10: thermoregulation- Rosen > Flashcards

Chapter 10: thermoregulation- Rosen Flashcards

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USMLE® Step 1 flashcards
1
Q

Heat is produced in large part by? What is the primary source

A

oxidative metabolism, glucose is the primary source

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2
Q

most heat is generated by?

A

heat is produced in large part by oxidative metabolism

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3
Q

energy source for heat generation is?

A

glucose is the primary energy source and generates 686 Kcal/ mole.
energy can be in CHEMICAL or HEAT form

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4
Q

where is most of the body heat made?

A

“heat production is not generally uniform, with the internal organs contributing over 70% of the total heat production”

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5
Q

what kinds of things affect a person’s normal body temperature?

A

temperatures varies with a diurnal (circadian) rhythm or with menstrual cycle

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6
Q

body can only adjust heat when it is between __ and __ C

A

only when it is below 40C and above 30 C

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7
Q

what are the two categories of evaporation for heat loss

A

insensible evaporation ==> from expired air and diffusive from epidermis via stratum conium
sensible evaporation ==> from cholinergic sympathetic stimulation of sweat glands

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8
Q

how much heat is lost in sweat?

A

per day, you lose about 584 Kcal. Thats 1 L of sweat. I hope your laundry detergent works well. thats gross

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9
Q

what kinds of things are in your sweat?

A 
NaCl
KCl
urea
organic acid 
other trace electrolytes
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10
Q

humid and sweaty is bad because?

A

if the air is saturated, then the sweat cannot evaporate. So, sweat just drips off you without removing heat. (You basically did a lot of work for nothing AND you lost water/electrolytes)

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11
Q

Sensible evaporation

A

Sweating. Cholinergic sympathetic stimulation of sweat glands. Sweat is mostly dilute NaCl with some KCl, urea, organic acid and other electrolytes.

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12
Q

what is the important constant in the equation he gave us?

A

heat = (surface area) * (conduction) * ((skin temp.) - (other temp))
the important part here is the conduction value

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13
Q

why do we care about the conduction value?

A

this number is high for water, lower for air.

you lose body temperature via conduction MUCH FASTER in water than in air

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14
Q

you are cold, so you curl up. how does that help

A

you reduce your conductive surface area, therefore, lowering heat loss

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15
Q

what is convection

A

this is conductive heat loss made more efficient by blowing air around. you constantly blow cooler air to replace the warm air covering your skin

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16
Q

what radiates heat?

A

all objects with temperature greater than absolute zero….. I’m pretty sure that means everything above 0 Kelvin…. which is everything in the world

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17
Q

1 calorie

A

1g H20 from 0-1C

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18
Q

Combustion of glucose=

A

686kCal/mol as heat

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19
Q

Oxidative metabolism of glucose?

A

420 kCal/mol as heat

266kcal/mol as ATP high energy bonds

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20
Q

Heat production is mainly from (think on a larger scale, now).

A

Internal organs= 60%

internal organs= 6-7% body mass

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21
Q

Temperature varies with a _____

A

diurnal rhythm (day/night schedule)

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22
Q

At rest we make this much heat? During exercise?

A

1kcal/hour/kg (x10 during exercise)

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23
Q

Increases > ____ are damaging and potentially fatal

A

7-9F (4-5C)

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24
Q

2 sources or insensible evaporation. how much/day?

A
  1. saturation of expired air
  2. loss from stratum corneum (epidermis)
    =1L/day= 584kCal
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25
Q

What can increase heat/water loss?

A
  1. high altitude (due to increased ventilation)
  2. burns (no more stratum corneum)
  3. exposure of wet tissues during surgery
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26
Q

Sensible evaporation

A

Sweating. Cholinergic sympathetic stimulation of sweat glands.

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27
Q

When you are sitting in class, what % of heat loss is insensible evaporation

A

15%. the rest ( 85% is due to convection, radiation, conduction)
==> Dr. Walker, this is why the room needs to be warmer

28
Q

bidirectional heat transfer

A

this occurs for radiative and conductive/convective heat routes.

29
Q

unidirectional heat transfer

A

evaporative is ONLY for heat LOSS.

aka sweating is unidirectional

30
Q

dry air vs humid air?

A
  • normal body temp is more easily maintained at 38C/100F in relatively dry air
  • humidity makes sweating less efficient which means body starts warming up when air is 50F
31
Q

what is the best way to measure temp?

A

Oral and Anal are good (haha) but a pulmonary artery catheter is best ***doesn’t sound comfy. he suggests tympanic membrane temperature instead of that

32
Q

what can the superficial tissues do to regulate body heat?

A

“heat Xchange is dominated by conduction btn capillary blood and normally cooler skin surface”

aka… vasodilation of the skin

33
Q

what controls the skin’s heat loss?

A

the ANS/hypothalamus

34
Q

loss of body heat through skin is especially important for whom?

A

da leetle bebes. they havea so much skin and little bodies;
“ratio of body surface to weight is greater than in adults”

35
Q

where are temperature neurons

A
  • cutaneous thermoreceptors(skin)

- core thermo receptors (pre-optic area of hypothalamus; also spinal cord)

36
Q

what are the two types of temperature neurons

A
  • “certain neurons, distributed over the entire skin surface, can respond to either heating or cooling”
  • core “respond to direct heating or cooling of these areas”
37
Q

what are the three levels of regulation of heat?

A

vasomotor regulation
metabolic regulation
combined sudomotor/vasomotor regulation

38
Q

when do you use vasomotor temp regulation

A

mild thermal stress or exercise. Vasodilation/vasoconstriction.
also, during rest

39
Q

what type of regulation is shivering? is it effective?

A

it is metabolic.
its not terribly effective; muscles create heat (heat made 3xs regular amount), but you must vasodilate to get blood to those muscles= increased loss via convective/conductive

40
Q

what is the last resort response?

A

“elevation in body temp,. causes progressive increases in sweating and acitve vasodilation”

41
Q

what is fever?

A

when the hypothalamus changes the temperature set-point to a higher temperature.

42
Q

how do you distinguish fever.

A

the body has a normal circadian temperature rhythmicity (lowest values at pre-dawn, highest in early evening). For a low grade feefer, you must monitor the temp for 24 hours to determine if its normal or not

43
Q

pyrogen=

A

chemicals that cause a febrile response. they can be:
1- EXogenous (from bacteria)
2- ENDogenous (from your cells

44
Q

what are the EXogenous types of pyrogens

A

high MW polysaccharides from gram negative bacteria. work by activating endogenous pyrogens.

45
Q

what are the ENDogenous types of pyrogens?

A
  • “interleukin 1 beta is currently thought to be the most important”
  • tumor necrosis factor (secreted by macrophages in response to gram -)
  • prostaglandin E2
46
Q

what does interleukin 1 beta do

A
  • produce fever by direct action on the hypothalamus
  • activate the immune system
  • release neutrophil from marrow
  • increase antibody production
47
Q

Prostaglandin E2 is important in?

A

there is some debate on whether or not it causes fever. either way, “aspirin, an anti-pyrogenic, inhibits its synthesis”

48
Q

fever from a broken hypothalamus?

A

nope. not usually. thats what they used to think though.

49
Q

how could you break your hypothalamus

A

tumor or hemorrhage. To test this hypotheisis, give the patient barbituates (CNS depressant). if it lowers body temperature, then the hypothalamus is broken. this is a “central temperature problem”

50
Q

animals helped us prove what about fevers?

A

animals that allowed their temperature to stay increased during infection had a better survival than those that were cooled.

51
Q

hyperthermia is found to help with?

A

anthrax
pneumococcal pneumonia
leprosy
various fungal, viral, rickettsial disease

52
Q

what causes elevation of body temperature? (in general)

A

excessive heat production
diminished heat dissipation
hypothalamic dysfunction
look at the chart for specific examples

53
Q

what is the ANS respose to hyperthermia?

A
  • during higher temperature, cardiac output increases so it can get more blood to skin for cooling.
  • in apical regions like hands and feet you inhibit vasoconstriction for heat loss
  • in other regions you actively vasodilate
54
Q

heat stroke is from

A

poor heat dissipation due to poor evaporative cooling

55
Q

net result of heat stroke?

A

dehydration
hyperthermia
dropped BP
lower electrolytes

56
Q

how do you treat heat stroke? (home rememdy)

A

give ELECTROLYTES!! if you just give them water you DILUTE the already small level of electrolytes they have

57
Q

exertional heat stroke you need to think about?

A

they body is hot AND it has exceeded the hearts ability to pump blood for cooling

58
Q

net result of exertional heat stroke

A

they vasodilated and are using their muscles, so the blood is NOT central. you can get a “disasterous drop in BP regulation” *** add in the other heat stroke symptoms and that doesn’t sound too great

59
Q

how do you treat either type of heat stroke in a hospital?

A

physical cooling (fans, wipe them down with a wet cloth)
IV saline and potassium
**anti-pyretics (aspirin) are NOT useful here because the hypothalamus didn’t turn up the heat

60
Q

hypothermia does what

A

general CNS depression, so the hypothalmus isn’t able to compensate.

61
Q

what temperature is hypothermia

A

below 90 F

62
Q

when do you use hypothermia on purpose? why?

A

surgical procedures (like heart things) to reduce oxygen demand, reduce BP, reduce bleeding

63
Q

lungs?

A

are done!!!! last card!!!

64
Q

t/f body is a source of radiant energy

A

True

65
Q

Majority of heat loss when temp>95F

A

evaporation

66
Q

What happens to blood flow to CNS in hyperthermia

A

decreases, more flow to skin so it can be cooled.

medical physiology (9 decks)

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