W6 - Thermoregulatory System Flashcards by Holly Tomlinson

Contributing factors to heat loss

Radiation

Conduction

Convection

Evaporation

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How does heat conservation happen?

When blood is quickly shunted to the deep cranial, thoracic + abdominal cavities.

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Contributing factors to heat gain

BMR

Muscular activity

Hormones

Thermic effect of food

Postural changes

Environment

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During heat conservation, why is blood rapidly shunted to the deep cranial, thoracic + abdominal cavities?

To optimise insulation from subcutaneous fat + other components of the bodys shell.

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What does an increase in internal heat do to the bodys peripheral vessels?

Dilates them as warm blood flows to the cooler periphery.

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What contains the central coordinating centre for temperature regulation?

Hypothalamus

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What are the 2 ways in which the bodys heat-regulating mechanisms can be activated?

Thermal receptors in skin

Changes in temp of blood that perfuses the hypothalamus

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Where do the thermal receptors in the skin provide input to?

Central coordinating centre in hypothalamus

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What plays the primary role in maintaining thermal balance?

The central hypothalamic regulatory centre

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What do cells in the anterior portion of the hypothalamus detect and what do they receive?

Slight changes in blood temp

Receive peripheral input.

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What is the result of the cells activity in the anterior portion of the hypothalamus being heightened?

In regards to the anterior hypothalamus

Initiates coordinated responses to facilitate heat loss = cooling

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What provides as the primary monitoring system to asses body warmth?

Temp of blood that perfuses the hypothalamus.

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What are the organism types for thermoregulation?

Homeotherms

Endotherms

Ectotherms

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Define homeotherms

Have a constant internal body temp regardless of external stimuli

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Define endotherms

Generate heat internally

Maintain high basal heat prod

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Define ectotherms

Depend on external heat sources

Temp changes w/ env

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What is our core body temp?

36.5-37.5

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What is the optimal function for our temp?

36.5-40.0

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When can hypothermia be established?

When body temp is <35.0

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What is the lowest survivable internal core temp?

~14.4

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Effects from hypothermia

Loss of motor skills

Shivering

⬇️ blood circulation

⬇️ skin temp

Confusion/fatigue

Loss of consciousness

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When can hyperthermia be established?

When body temp is >38.0

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What is the highest survivable internal core temp?

~46.5

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At what body temp does damage to cells occur?

42.0 + above

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Biggest effects of hyperthermia

Heat exhaustion Heat stroke

Symptoms of heat exhaustion

Faint/dizzy Excessive sweating Cool, clammy skin Nausea Rapid,weak pulse Muscle cramps

Symptoms of heat stroke

Throbbing headache No sweating Red, hot, dry skin Nausea Rapid, strong pulse

Factors affecting core body temp

Body morphology Environnent Skin Metabolic heat production

What comes under body morphology?

Body mass Body composition

Factors affecting core body temp What comes under skin?

SA Temp Skin wettedness

Factors affecting core body temp What comes under environment?

Temp Humidity Air velocity Air density Clothing properties

Define specific heat capacity

Amount of energy req to raise the temp of a given substance by 1 degree celsius

What are the 2 types of heat production?

Voluntary Involuntary

What comes under voluntary heat production?

Exercise

What comes under involuntary heat production?

Shivering Hormones (thyroxine + catecholamines)

How many kJ of heat does 1l of O2 produce?

~20kJ

How can you measure core body temp?

Using thermometer probe

Where can the thermometer probe be used to measure core body temp

Hypothalamus Oesophagus Rectum Intestinal Oral under tongue Ear drum

What does measuring skin temp depend on?

Ambient temp Distance from core Skin bf

In what ways can we externally gain heat?

Sky thermal radiation Solar radiation Ground thermal radiation

What does the thermal gradient state?

Heat transfer is always from higher to lower temps

% heat loss at rest from evaporation

~25

% heat loss during exercise from evaporation

~85

How many kJ of heat comes from 1g of sweat?

2.41

When sweating, what are the sweat glands stimulated by?

Sympathetic nervous system. (SNS)

What factors influence evaporation + how?

Air temp (humidity) = ⬇️ it Convection currents (winds) = ⬆️ it Skin exposure = ⬆️ it

How is sweat loss calculated?

Change in mass + fluid intake - urine

What does the sweat rate depend on?

Body size Absolute VO2 Aerobic fitness Heat acclimatisation Env

Define radiation

Transfer of heat in form of electromagnetic waves

% of heat loss at rest at room temp from radiation

~60

Define conduction

Heat transfer from body to object w direct contact

% of heat loss at rest at room temp from conduction

Define convection

Heat transfer from 1 place to another by movement of fluids (air/H20)

% of heat loss at rest at room temp from convection

~12

What happens to heat dissipation by convection during exercise?

Reduced

Actions of the hypothalamus following hypothermia

Cutaneous vasoconstriction Shivering Catecholamine release Thyroxin release

Areas of body w. greater heat loss

Skull Groin Armpits Extremities

What does hyperthermia do to sprint + power performance?

Improves it

How does hyperthermia improve sprint + power performance?

⬇️ resistance of muscles/joints Faster nerve conduction velocity Improvement in muscle contractile elements Faster metabolic rate ⬆️ SNS activity

Define Q10 temp coefficient

Measure of rate of change of system as a consequence of increasing temp by 10C.

What does hyperthermia do to endurance performance?

Impairs it

What does hyperthermia do to repeated sprint ability?

Impairs it

Overall why is performance impaired by ⬆️ core temp + sweat rate?

⬇️ plasma vol ⬇️ blood vol ⬇️ venous return ⬇️ end diastolic vol

Cognitive consequences of core temp ⬆️

Fatigue perception ⬆️ Impairment in: Scanning vigilance Reaction time Attention Visual motor tracking

Order of warning signs for hyperthermia

Heat cramps --> Heat Exhaustion --> Heatstroke

Treatment to heat exhaustion

Cooler env Elevate feet Saline (orally or intravenous)

Treatment for heat stroke

Cold water Ice bath Wet towels

Methods to reduce hyperthermia during exercise

Heat acclimatisation

Effects of heat acclimatisation

⬇️ body temp at given heat ⬆️ sweat rate + more dilute ⬇️ Skin bf = ⬆️ to muscles SV maintained

What is the result to the stimulation of cutaneous cold receptors?

Constricts peripheral bv = ⬇️ bf of warm blood to bodys cooler surface + redirects it to warmer core.

What does shivering do?

Generates metabolic heat

Thryoxine

Thyroid hormone that ⬆️ resting metabolism

What 2 competitive CV demands does the body encounter when exercising in the heat?

1. Muscles req delivery of arterial blood to sustain energy metabolism 2. Arterial blood diverts to periphery to transport metabolic heat for cooling at skin surface (this blood can't deliver O2 to active muscle)

What effect does ageing have on thermoregulation?

Delays onset of sweating + blunts the magnitude of the sweating response in 1 of 3 ways.

What are the 3 ways in which ageing can blunt the magnitude of the sweating response?

1. Modified sensitivity of thermoreceptors 2. Limited sweat gland output 3. Dehydration-limited sweat output w. insufficient fluid replacement

Functions of the posterior portion of the hypothalamus

⬆️ blood pressure Shivering or body heat conservation (thermoregulation).

What does damage or destruction to the posterior region of the hypothalamus cause?

Hypothermia