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*Neuroendocrine Exam 3 > 6. Thermoregulation > Flashcards

6. Thermoregulation Flashcards

1
Q

Avg. body temperature:

A

36.7 celcius, 98.06 F.

Lower in morning and increases throughout the day.

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2
Q

Which areas change the most in temperature due to the environment?

The least?

A

Hands, feet.

Core, oral, then skin.

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3
Q

Enzyme that temperature effects?

A

Q10

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4
Q

Core thermoreceptors locations

A

Brain, skin, viscera

-different locations tell brain about different temps

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5
Q

Cutaneous thermoreceptors:

What can they detect?

What are they most sensitive to?

What do they tell us?

A

Axons in skin.

Bimodal (temp and touch, etc).

warm or cold; 10x as many cold sensitive.

Tell us about the environmental conditions.

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6
Q

Why is there thermoreceptors in the gut?

Where do they relay this info?

A

Threats to maintenance (cold, hot food, etc).

Hypothalamus.

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7
Q

Where are the thermoreceptors in the brain (hypothalamus)? (2)

What are these most sensitive to?

Where do they relay the info?

A

Pre-optic region of hypothalamus
Superoptic region of hypothalamus

3x as many warm sensitive.

Other parts of hypothalamus.

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8
Q

“Hypothalamus has connections to control…” (3)

A

Hormonal, autonomic and behavior changes that are part of thermoregulation.

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9
Q

3 big roles of hypothalamus for controlling temperature

A
  1. Determine set point
  2. Receive info about current info
  3. Decide what to do
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10
Q

What can change set point? (2)

A

Core temp changes.
Sleep –> decrease set point.
Exercise –> increase in set point.

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11
Q

Which part of the hypothalamus responds to heat?

Which part responds to cooling?

Then, what do these parts do?

A

Anterior responds to heat. Begins heat loss behaviors.

Posterior responds to cooling. Begin heat production behaviors.

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12
Q

Why is adipose tissue so important in babies?

A

Because their surface area is large, so they lose heat easier. Adipose helps insulate.

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13
Q

4 mechanisms of heat production

A
  1. ANS
  2. Endocrine (thyroxine, Epi)
  3. Muscular activity (shivering, moving around, etc)
  4. Non-shivering thermogenesis
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14
Q

What triggers shivering?

What triggers an increase in voluntary activity?

A

Dorsomedial posterior hypothalamus–> increases motoneuron excitation

Cortex

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15
Q

What does BAT need to be activated?

What is the process?

A

BAT needs adrenergic innervation.

Uncoupling protein allow for low efficiency hydrolysis of ATP and leads to more heat production.

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16
Q

Insensible heat loss is:

Sweating heat loss is:

There are what types of heat loss?

A

Respiratory

Controlled; ant pituitary; stimulated from cholinergic sympathetics and catecholamines (epi/NE, AD to decrease sodium loss and acclimate)

Evaporative

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17
Q

Convection

Conduction

Radiation

A

Movement of molecules away from contact (air heating and rising).

Transfer of heat between objects that are in contact.

Transfer of heat between objects not in physical contact (person and wall).

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18
Q

How can heat be loss by circulation?

A

Anastomoses at the surface of the skin allow heat to move from blood to external environment.

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19
Q

Innervation to sweat glands (it is unusual)

A

Sympathetic cholinergic.

ACh binds mAChR

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20
Q

What happens as fluid travels from sweat gland to external environment, generally?

A

Na+, Cl- and water are reabsorbed

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21
Q

Low flow rate through duct (not too hot) ensures what kind of sweat?

A

Salty. Lots of water is reabsorbed and Na+ is high.

22
Q

High flow rate through duct (very hot) ensures what kind of sweat?

A

Diluted, high H20. Low water reabsorption and w/ acclimation little sodium due to aldosterone action.

23
Q

Fever

A

Controlled increase in temp directed by hypothalamus

24
Q

How does an infection change the set point?

A

The bug secretes endotoxins and immune cells secrete cytokines which activates PGE2.
PGE2 acts on hypothalamus which activates systems to produce heat in order to match a new higher set point

25
Q

If T set point > Tb, what 2 things happen?

A

Increase heat production.

Decrease heat loss.

26
Q

How does T set point dip below T body in an infection?

A

The bug is gone and no more endotoxins.

Now Tb > T set point and we try to cool off.

27
Q

body temp range

A

36.3-37.1 C

28
Q

what is a stimulus for TRH release by the hypothalamus?

A

cold (non-shivering thermogenesis)

29
Q

3 factors involved in non-shivering thermogenesis

A
  1. hormonal influence (thyroxin & epic increases metabolic rate)
  2. increase food intake = increase metabolism
  3. BAT: adrenergic innervation for initiation
30
Q

What activates and innervated BAT?

A

activates: circulating epi
innervates: sympathetic fibers

31
Q

2 steps in sweating process

A
  1. serum filtration (plasma, Na, Cl)
  2. reabsorption: fluid goes thru gland to skin, H20, Na+, Cl
    - dependent on flow rate
32
Q

how do you regulate set point and body temperature during a fever? (T-body>T-set)

A

TB: decrease heat production

  1. apathy/inertia: move less, create less heat
  2. anorexia via hypothalamus feeding centers b/c food intake increase metabolism

T-Set Pt: increase heat loss

  1. conduction/convection
  2. EHL (sweat)
  3. insensible heat loss (pant)
33
Q

how do you regulate set point and body temperature during hypothermia? (T-body

A

decrease core temp
T-Body: increase heat prod
-Shivering and non-shivering thermogenesis

T-Set Pt: decrease heat loss

  1. Vasoconstrict: blood away from skin
  2. Decrease EHL
34
Q

how does T set point increase beyond T-body during an infection?

A

the endotoxins and cytokines stimulate prostaglandin E2 which increases the hypothalamic set point for temp –> stimulating and increase in heat production and decrease in heat loss = FEVER

35
Q

defined the controlled variable in thermoregulation

A

variable that system is trying to control, here its temp

36
Q

defined the sensor in thermoregulation

A

device that measures controlled variable, here its the hypothalamus

37
Q

defined the set point in thermoregulation

A

ideal value of the controlled variable

38
Q

defined the controller in thermoregulation

A

device controlling set point to the actual value of controlled variable

39
Q

defined the effectors in thermoregulation

A

how we change the controlled variable

  • ANS (parasym when hot; symp when cold w/ 1 exception)
  • Hormonal (thyroxin and epi/NE when cold)
40
Q

what is a negative feedback system

A

stable system; designed to minimizes changes, all effectors are activated to return controlled variable back to set point

41
Q

what is a positive feedback system

A

system designed as such that the effector pushes the controlled variable away from set point once it starts to change
-ex: pushes Tbody away from Set Temperature, decrease in core temp occurs due to heat loss behaviors (As I lose head, my body temp drops further from set and this difference will get larger)

42
Q

what is a feed-forward system

A

controlled system that prevents change rather than response to change
-here, have sensory that detect threats to room temp, rare in body

43
Q

what fibers are associated with thermoreceptors

A

increase temp: c-fibers, b/c they’re free nerve endings

decrease temp: a-delta

44
Q

what proteins render thermoreceptors sensitive to cold temp?

A

10-38 C
TRPM8: cold and menthol
TRPA1

45
Q

What 4 receptor channels respond to heat? list from highest to lowest temps

A
  1. TRPV-2 (>52 C)
    * 2. TRPV-1(>43 C): responds to damaged heat, capsaicin, Na or K enter cell
  2. TRPV-3 (>31 C)
  3. TRPV-4 (>25 C)
46
Q

what 2 receptor channels respond to cold?

A
  1. TRPM-8: cold and menthol, opens similar to TRPV-1

2. TRPA1

47
Q

Causes of fever

A
  1. brain damage
  2. infection response (pyrogens)
  3. cytokine production- act through OVLT b/c cannot cross BBB
48
Q

what enzyme produces prostaglandins and what are it’s 2 forms?

A

Cyclooxygenase (COX)

  1. COX1: all tissues, involved in norm function
  2. COX2: produced from immune cells, inflammation and fever
    - both inhibited by aspirin and ibuprofen
49
Q

What are 2 reasons that sweating would stop during circulatory shock during heat stroke?

A
  1. loss of body water to pt that body cannot sweat anymore (so if dehydrated, develop heat stroke at lower temps)
  2. thermoregulatory failure of hypothalamus
50
Q

How does hypothalamus control ANS?

A
  1. info about cortisol levels from limbic system
  2. ascending inputs from nucleus tracts solitaires (resp, CV, GI control) and nucleus ambiguus (CV and resp control) - control via paraventricular nucleus
51
Q

where are thermoreceptors whose discharge remains virtually constant over a wide range of environmental temperatures located?

A

hypothalamus

52
Q

what would inhibition of the dorsomedial posterior hypothalamus cause?

A

inhibit shivering, detrimental if hypothermic

*Neuroendocrine Exam 3 (27 decks)

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