Temperature regulation Flashcards
What is temperature?
Heat energy that an object possesses
What is a cal?
Heats 1g of water by 1 degree
How many joules is in a cal?
4.2
How many cal are in a kcal?
1000
How many calories does 1mL of oxygen burn?
5
Range of ideal body temperature
36.5-37.5
What is hypothermia?
<35 degrees
What is hyperthermia?
> 38 degrees
What is pyrexia?
Hyperthermia
What happens when body temperature reaches 35 degrees?
Shivering, peripheral circulation shutdown
What happens when body temperature reaches 33 degrees?
Confusion, drowsiness
What happens when body temperature reaches 31 degrees?
Unconscious, risk of arrythmia
What happens when body temperature reaches 29 degrees?
Respiratory muscle failure
What happens when body temperature reaches 27 degrees?
Death
What happens when body temperature reaches 39 degrees?
Sweating, vasodilation, breathless
What happens when body temperature reaches 40 degrees?
Vomiting, dehydration, weakness
What happens when body temperature reaches 41 degrees?
Fainting, confusion, drowsiness
What happens when body temperature reaches 42 degrees?
Brain proteins denaturing
What happens when body temperature reaches 43 degrees?
Death
Characteristics of cold receptors
Peripheral in skin, conducted via myelinated A fibres
Characteristics of warm receptors
Central in hypothalamus with few in skin
What do nociceptors do?
Identify extremes in temperature, perceive it as pain
What are behavioural responses?
Voluntary actions to increase muscle activity or change body’s immediate environment
What are physiological responses?
Involuntary actions to increase muscle activity or change body’s immediate environment
What is the thermoneutral zone?
Band within which normothermia can be maintained using basal energy production without evaporative heat loss
Neurological responses
Sympathetic NS (vasomotor tone, sweating) and motor system (shivering)
Hormonal responses
Thyroid (produces thyroxine) and adrenal medulla (produces adrenaline)
What is a MET?
A measure of basal metabolism
Metabolic Equivalent of Task
How many METs are in walking?
2-4
How many METs are in cycling?
6-8
How many METs are in sprinting?
10-12
How much heat is lost through skin?
90%
What is conduction?
Direct contact with adjacent material
What is convection?
Warms adjacent air, creates heat-losing current
What is radiation?
Transfer through infrared rays to distant objects at lower temperature
What is evaporation?
Latent heat of vaporisation lost as sweat/respiratory humidity evaporates
Where does sweating occur?
Eccrine/merocrine glands
Which system controls sweating?
Sympathetic NS
Which neurotransmitter is in sweat glands?
ACh not NA
What is a fever?
Elevated temperature from infection or inflammation
What are pyrogens?
Cytokines (Il-1, Il-6, TNF-alpha) released by macrophages. They travel to the hypothalamus to add higher value and act via PGE2
What is heat stroke?
Rapid, extreme temperature rise, usually exercise related but can be exacerbated by drugs
Why are neonates at high risk of hypothermia?
High surface area to weight ratio, unable to make behavioural changes
What is brown fat?
Heat source used by neonates, found between scapulae
Oxidative metabolism in mitochondria is uncoupled to phosphorylation and produces heat rather than ATP. Activated by thyroid hoemones sensitizing adipocytes to action of adrenaline
Why is near-drowning a risk factor for hypothermia?
Increase in heat lost by conduction
Why is a drug overdose a risk factor for hypothermia?
Reduced metabolism and heat production, can’t make behavioural changes
Why is major trauma a risk factor for heat loss?
Exposure increasing heat loss, replacement of blood lost with cold fluid
What is induced hypothermia?
Reduced metabolic requirements (e.g. during surgery) achieve by surface cooling and cardio-pulmonary bypass
Ways to increase temperature
Warm clothing, vaso-constriction, T3 release, catecholamine release, shivering
Ways to decrease temperature
Sweating, vasodilation, exposure, decreased muscle activity
