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Neuro Endo 3 > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

Mechanisms of Heat Production

A

ANS (sympathetic)
Endocrine (thyroxine, epinephrine)
Muscular Activity
Non-Shivering thermogenesis

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2
Q

Shivering location

A

dorsomedial posterior hypothalamus

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3
Q

Function of shivering

A

increase motoneuron excitation to produce heat

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4
Q

Location of voluntary action to produce heat

A

Cortex

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5
Q

What is normal body temperature? (morning)

A

36.7 C (98.06 F)

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6
Q

What is the normal range of body temperature? (morning)

A

36.3-37.1 C

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7
Q

What is the flow of control systems for thermoregulation?

A

Set point determined by controller acts on effector which changes the core temperature. Core temperature is measured by a sensor that then relays this information back to the controller to see if any adjustments need to be made.

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8
Q

How does core temperature vary?

A
  • varies 1-2 C over 24 hour period
  • lowest at 6am
  • highest during early evening
  • circadian rhythm
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9
Q

What does current body temperature affect?

A
  • CoQ10 activity which generates energy via electron transport chain
  • cellular function
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10
Q

What does environmental temperature affect?

A

-threatens body temperature as body is always generating heat

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11
Q

What is the function of core thermo receptors?

A

Located in the brain and viscera

In the viscera- tells body about core temperature and tells hypothalamus about possible threats to core temperature via food eaten
(i.e. shivering when eating ice cream)

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12
Q

What is the function of cutaneous thermo receptors (skin)?

A

Bimodal (temperature and touch sensitive)

May be warm or cold sensitive

10x as many cold sensitive because at skin level, cooling off is bigger threat to survival

Tell us about environmental conditions

Feed forward system: If I don’t do something, this will happen, so I’ll respond now to prevent that

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13
Q

Where do thermo receptors send signals and what occurs there?

A

Pre-optic and superoptic regions of hypothalamus

Contain neuron cell bodies sensitive to changes in temperature (3x as many warm sensitive)

Relay information to other areas of hypothalamus

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14
Q

What is the controller of thermoregulation in the body and how does it do this?

A

Hypothalamus

Connections to the hormonal, autonomic, and behavioral changes that are a part of thermoregulation

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15
Q

3 main jobs of hypothalamus

A

1) determine set point
2) receive info about current temp
3) decide what to do

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16
Q

How does the set point change with conditions?

A

Sleep: body temperature decreases; decreases the set point

Exercise: body temperature increases; increases set point

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17
Q

Function of Anterior Hypothalamus

A

Responds to heat

Heat loss behavior (cooling)

(Think AC)

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18
Q

Function of Posterior Hypothalamus

A

Responds to cooling

Heat production behavior

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19
Q

What are the challenges to thermoregulation in response to changes in environmental temperature?

A

Babies have high surface area in proportion to size so lose heat easily

Both anaerobic and aerobic metabolism generates heat as a by product

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20
Q

What are examples of non-shivering thermogenesis?

A

1) Hormonal influence: cold stimulates TRH release > thyroxin > increased metabolic rate; epinephrine
2) Increased food intake leads to increased metabolism
3) Brown adipose tissue: adrenergic innervation (sympathetic) for initiation

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21
Q

Function of Brown Adipose Tissue

A

Low efficiency hydrolysis of ATP via uncoupling proteins leads to more heat production (less energy produced, more dissipated as heat)

Innervated by sympathetic fibers and activated by epinephrine

22
Q

How is heat lost?

A

Evaporative heat loss: energy (heat) lost as water evaporates

23
Q

What are the two kinds of evaporative heat loss?

A

Insensible (respiratory)
Sweating (controlled)

Dogs also use panting as a form of heat loss since they cannot sweat

24
Q

Convection

A

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

25
Q

Conduction

A

Transfer of heat between object in physical contact with one another

26
Q

Radiation

A

Infrared radiation transferring heat between 2 object not in physical contact (loosing heat to the walls in the room)

27
Q

How does blood supply to the skin affect heat loss?

A

To lose heat, more blood is sent to the skin

Results in the flushing of skin when people are warm and trying to cool down; when people are cold, they turn pale as blood flow is decreased to the skin so they can maintain warmth at their core

28
Q

Characteristics of sweat glands

A

Lots of blood vessels nearby

Coiled region by the blood vessel

Duct leading to skin for exit of fluid

29
Q

Sweat gland innervation

A

Sympathetic cholinergic

NT: acetylcholine

Receptor: MUSCARINIC (note this is different than other sympathetic receptors)

30
Q

Steps of sweating:

A

1) filtration of serum, including the ions (Na+, Cl-)
2) as fluid travels up to the skin surface, water and sodium reabsorbed back into the blood stream in the duct of the sweat gland

31
Q

Rate of sweating when really hot

A

High flow rate: lots of water released since epithelial cells cannot reabsorb Na+ or Cl- fast enough, so less water is reabsorbed and more is released as sweat

32
Q

Rate of sweating when not terribly hot

A

Low flow rate: sweat is more concentrated because body has time to reabsorb a lot of the water it produced; sodium does not follow water back

33
Q

Acclimatization of Sweat

A

Increases sweat loss

Removes heat faster

Increases aldosterone secretion to minimize loss of Na+

34
Q

Response to Low Body Temp

A

Response initiated in Posterior Hypothalamus

Increase heat production:

1) behavior- motor activity
2) hunger- induce metabolism by eating
3) hormonal- TSH, catecholamines
4) Non-shivering thermogenesis
5) shivering (dorsomedial posterior hypothalamus activated)

Behavioral Changes:

1) curling up
2) increase clothing
3) piloerection (hair rising, goosebumps)

Decrease Heat Loss:

1) vasoconstriction (stimulation of posterior hypothalamic sympathetic centers)
2) decreased blood flow through venous plexus

35
Q

Response to Increased Body Temp

A

Response initiated by Anterior Hypothalamus

Decrease Heat Production:

1) apathy/inertia- less movement
2) anorexia - less food ingestion = less metabolism

Increase Heat Loss:

1) vasodilation to increase blood flow to give up heat through radiation
2) sweating
3) increased respiration

36
Q

What is a fever?

A

Increase in body temperature produced by the hypothalamus

37
Q

What are the causes of a fever?

A

Brain damage

Response to infection via production of cytokines (IL-1 beta, IL-6, beta-IFN, gamma-IFN, TNF-alpha)

Cytokines = peptides and cannot cross BBB, so act on OVLT which is near hypothalamus

38
Q

Making Fever

A

1) increased set point due to pyrogen
2) prostaglandin E2 produced in or near hypothalamus causes change in set point via EP3 receptor
3) set point increased, but body temp has remained the same
4) initiate heat generation
5) decrease heat loss
6) person perceives to be cold

39
Q

During Fever

A

1) body temp = set point
2) the “bug” is vanquished; no more endotoxins
3) no more activation of immune system
4) Hypothalamic set point returns to normal (lowers it from before)

40
Q

Resolution of Fever

A

1) now the body temperature is higher than the set point that was just lowered in the absence of endotoxin
2) brain perceives body to be hot
3) initiate heat loss responses
4) decrease heat production
5) fever “breaks”

41
Q

What controls access to autonomic nervous system?

A

Hypothalamus

42
Q

Where does hypothalamus receive descending influences from?

A

Cortical levels (i.e. Limbic system to produce changes seen during emotions)

43
Q

Where does hypothalamus receive ascending inputs from?

A

Nucleus Tractus Solitarius: respiratory control, cardiovascular control, gastrointestinal control

Nucleus Ambiguus: cardiovascular control, respiratory control

44
Q

What is the main hypothalamic nucleus and its neurons?

A

Paraventricular Nucleus:

1) Magnocellular- oxytocin and vasopressin
2) Paravocellular- releasing hormones
3) autonomic controlling

Bilateral outflow to both sympathetic and parasympathetic

45
Q

Fibers associated with nociceptors and thermo receptors

A

C fibers (small, unmyelinated, warm sensitive)

A-delta fibers (sparsely myelinated, small, cold sensitive)

46
Q

What are the proteins that render the thermoreceptors sensitive to temperature a member of?

A

Transient Receptor Potential Family (TRP)

47
Q

TRP-V1

A

V = Vallinoid- capsaicin

Firing rate increases as temp goes up

48
Q

TRP-M8

A

M = menthol

Firing rate increases as temperature goes down

49
Q

Negative Feedback

A

Any deviation from set point is returned to normal

Stable

50
Q

Positive Feedback

A

Any deviation from set point drives the variable further away from set point

Unstable

Ex) blood clotting, ovulation

51
Q

Feed Forward

A

Input not directly related to controlled variable can initiate a response

Prevent change by responding to the thing that can cause the change, not the change itself

Neuro Endo 3 (13 decks)

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