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NE Exam 3 > Thermoregulation > Flashcards

Thermoregulation Flashcards

1
Q

Negative Feedback System
(1) Sensors?
(2) What do sensors detect?
(3) Does the controlled variable change before the system activates?
(4) Effectors?
(5) Purpose

A

(1) Yes
(2) The controlled variable (ex. room temp)
(3) Yes
(4) Yes
(5) Return controlled variable to set point

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2
Q

Feed-Forward System
(1) Sensors?
(2) What do sensors detect?
(3) Does the controlled variable change before the system activates?
(4) Effectors?
(5) Purpose

A

(1) Yes
(2) Threat to the controlled variable (ex. external temp)
(3) No
(4) Yes
(5) Keep controlled variable form leaving the set point; prevents change

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3
Q

Core Temperature

A
  • Temperature of the viscera and the brain (particularly the hypothalamus)
  • Typically 36.3 - 37.1 C
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4
Q

Changing Core Temperature over time (days) is produced by:

A

Circadian Rhythm

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5
Q

Thermoreceptors that tell us about core temperature:

A
  • Brain
  • Viscera
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6
Q

Cutaneous Thermoreceptors

A
  • Axons located in skin (bare nerve endings)
  • Tell us about environment temperature
  • Often bimodal (temperature and touch sensitive)
  • May be warm or cold sensitive (10x more cold sensitive than warm sensitive)
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7
Q

Why are there thermoreceptors in the gut?

A
  • Called Visceral Receptors
  • Component of core temperature
  • Food poses a threat to core temperature (ex. cold food can lower core temp)
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8
Q

Hypothalamic Thermoreceptors

A
  • Located in Pre-Optic and Superoptic Region of Hypothalamus
  • Neuron cell bodies sensitive to changes in temperature
  • 3x as many warm sensitive compared to cold sensitive
  • Relay their information to other areas of hypothalamus
  • Detect core temperature
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9
Q

___ has connections to control the hormonal, autonomic, and behavioral changes that are part of thermoregulation

A

Hypothalamus

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10
Q

Response to Heat:

A

Anterior Hypothalamus

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11
Q

Response to Cooling:

A

Posterior Hypothalamus

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12
Q

Dorsal Longitudinal Fasciculus (DLF)

A
  • Plays major role in autonomic regulation
  • Main output from hypothalamus
  • Associated hypothalamic nucleus: Paraventricular Nuclei
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13
Q

Outputs of DLF (where axons synapse):

A
  • PAG
  • Parabrachial Nucleus
  • Mesencephalic Raphe Nucleus
  • Locus Ceruleus
  • Dorsal Moror Mucelus of the Vagus*
  • Nucleus Ambiguus*
  • Parasympathetic and sympathetic neurons in spinal cord*

Also provides inputs from locus ceruleus, parabrachial nuclei and PAG to the Paraventricular Nucleus

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14
Q

Medial Forebrain Bundle

A
  • Plays role in autonomic regulation
  • Provides substantial inputs to the hypothalamus, especially from the nucleus tractus solitaries (sensory info)
  • Outflow from hypothalamus goes to same nuclei as DLF
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15
Q

Mammillotegmental Tract

A
  • Plays role in autonomic regulation
  • Smaller than Medial Forebrain Bundle and DLF
  • Mammillary Bodies –> Autonomic Nuclei
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16
Q

Hypothalamic Regulation of the ANS

A
  • Significance: in order to control body temp the hypothalamus must be able to regulate the ANS
  • Major outflow from Hypothalamus: Paraventricular Nucleus
  • Major tract: DLF –> Autonomic Nuclei
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17
Q

Warm Thermoreceptors:

A

TRP V1

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18
Q

Cold Thermoreceptors:

A

TRP M8

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19
Q

What happens to Core Temperature when sleeping?

A

Decreases – decreased set point by Hypothalamus; tied to circadian rhythm

20
Q

What happens to Core Temperature when exercising?

A

Increases (can get as high as 40 C) – increased set point by Hypothalamus

21
Q

Why do babies lose heat better than adults?

A

They have a high surface area in proportion to their size which means they lose heat easily; layer of subcutaneous fat is critical in helping them maintain their core temp

22
Q

Mechanisms of Heat Production:

A
  • ANS (esp SNS)
  • Endocrine (Thyroxine, Epinephrine)
  • Muscular activity
  • Non-shivering thermogenesis
23
Q

Heat Production: Shivering

A
  • Mediated by Dorsomedial Posterior Hypothalamus
  • Increase in motorneuron excitation
24
Q

Heat Production: Increase Voluntary Action

A
  • Hypothalamus sends signal to cortex saying we are cold and need to start moving
  • Why people unconsciously fidget, jump, move when cold
25
Q

Heat Production: Non-Shivering Thermogenesis

A
  • Strong hormonal influence – thyroxin increases metabolic rate; cold can increase TRH release; increased Epinephrine release from Adrenal Medulla
  • Increase food intake –> leads to increase in metabolism
  • Brown Adipose tissue – adrenergic innervation for initiation
26
Q

Brown Adipose Tissue

A
  • Low efficiency hydrolysis of ATP via uncoupling proteins leads to more heat production than otherwise – ADP and Pi not used for anything other than heat production
  • Innervated by sympathetic fibers and circulating epinephrine
27
Q

Importance of Brown Adipose Tissue in Humans

A
  • Critical in infants for maintaining body temperature
28
Q

Evaporative Heat Loss

A
  • Energy (heat) lost as water evaporates
  • Two kinds: Insensible (respiratory), Sweating (controlled)
29
Q

Mechanisms of Heat Loss

A
  • Convection
  • Conduction
  • Radiation
30
Q

Convection

A

Movement of molecules away from contact; Air heating and rising

31
Q

Conduction

A

Transfer of heat between two objects in physical contact with one another

32
Q

Radiation

A

Infrared radiation transferring heat between 2 objects not in physical contact; Ex. losing body heat to the walls

33
Q

Sweat Gland

A
  • Lots of blood vessels nearby
  • Coiled region by vessels
  • Duct leading to skin
34
Q

Sweat Glands: Innervation

A

Sympathetic Cholinergic
- ACh is NT, binding to a muscarinic receptor which leads to increased blood flow and sweat production

35
Q

Steps of Sweat Production

A

(1) Sympathetic Cholinergic Innervation (Muscarinic Receptors)
(2) Filtration of serum, including the ions (from blood vessel to sweat gland)
(3) As fluid travels up to the skin surface, water and sodium are reabsorbed (taken back into the blood) in the duct of the sweat gland; flow rate depends on how much sweat you need and how acclimated you are)

36
Q

Sweating: Low Flow Rate

A
  • Concentrated
  • Little water b/c lots reabsorbed into blood vessels
  • High Na+ (didn’t follow water)
37
Q

Sweating: High Flow Rate

A
  • Lots of water lost – no time to reabsorb into blood vessels
  • With acclimation, little Na+ in sweat due to aldosterone action – as you get more used to a hot temp your sweat will get more profuse and dilute which prevents loss of too much Na+
38
Q

Ions absorbed along the duct of the sweat gland:

A
  • Na
  • Cl
  • Water
39
Q

The more acclimated to the heat I am, the ___ Na+ I reabsorb due to the hormone ___.

A
  • More
  • Aldosterone
40
Q

The less acclimated to the heat I am, the ___ Na+ I reabsorb

A

Less

41
Q

Integrated Responses: Decreased Core T (Tsetpoint > Tb)

A
  • Increase heat production (shivering, non-shivering thermogenesis)
  • Decrease heat loss (blood away from skin via vasoconstriction of superficial vessels, decreased EHL/sweating)
42
Q

Integrated Responses: Heat (Tb > Tsetpoint)

A
  • Decreased heat production (apathy/inertia, anorexia)
  • Increase heat loss (conduction/convection, EHL/sweat, insensible heat loss via panting)
43
Q

Fever
(1) Core Temperature
(2) Set Point
(3) Active Thermoregulatory Response
(4) Signs Present
(5) Subjective Perception
(6) Cause

A

(1) Increased
(2) Increased
(3) Heat production
(4) Pallor, shivering, behavioral changes associated with being cold
(5) Patient will often describe being cold
(6) Infectious agent producing inflammatory mediators acting in brain

44
Q

Hyperthermia
(1) Core Temperature
(2) Set Point
(3) Active Thermoregulatory Response
(4) Signs Present
(5) Subjective Perception
(6) Cause

A

(1) Increased
(2) Normal
(3) Heat Loss
(4) Flushed skin and sweating (may not occur if person is dehydrated), behavioral changes associated with being hot
(5) Patient describes being hot
(6) Increased heat production/decreased ability to eliminate heat

45
Q

Mechanism for Increase in Set Point for Temperature during Fever

A

(1) “Sick bug” secretes endotoxins, immune cells activated by the “bug” release cytokines
(2) Activation of Prostaglandin E2
(3) Binding to EP3 receptor
(4) Increase hypothalamic set point for temperature

46
Q

“Breaking” the Fever

A
  • Tb > Tset
  • Decreased heat production
  • Increased heat loss

NE Exam 3 (9 decks)

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