Thermoregulation And Pyrexia Flashcards
How does temperature vary in different circumstances
Core temperature is 0.5 degrees higher than surface (different sites)
Temperature also varies throughout the day (lowest in the morning)
Difference between the sexes and for women: ovulation sees a 0.5 degree increase
What are the receptors in the body used for thermoregulation
Thermal receptors are found not only in the skin but also in GI tract, great veins and hypothalamus and are specialised outgrowths of neurones
Information from these receptors is conveyed to the hypothalamus via the myelinated A delta fibres and unmyelinated C fibres
What is the coordinator of thermoregulation in the body
The anterior hypothalamus
Can trigger heat loss or heat production
Thermoregulation is dependent on internal homeostasis but can also be affected by….
Voluntary actions ( when we go out, where we go and how we dress) but this can’t be controlled by anyone such as elderly dementia patients or neonates in an incubator
Ways in which the body produces heat when feeling cold
- through metabolism = lots of reactions such as ATP production are not 100% efficient and are exothermic so produce heat
- shivering = uncoordinated fast activation of individual muscle units that can increase heat production by 5 times. Is metabolically expensive :( (requires a lot of glucose and oxygen) careful with septic patients
- brown adipose tissue = high numbers of mitochondria, when stimulated by beta-3 adrenoreceptors results in a lot of heat being produced when broken down
- vasoconstriction that is mediated by the sympathetic nervous system. Can alter heat loss by 8x
- paradoxical increased flow if prolonged cold exposure
- piloerection = erector pili contracts under sympathetic control for hairs to stand on end
- increased level of catecholamines such as Ad, NA that increase metabolism
Ways in which the body losses heat when too hot
Conduction/convection
Radiation
Evaporation
- sweating = located in dermis are sweat glands that are under sympathetic control. Gland tries to retain Na and naturally water so a lot of what is excreted is urea —> odour as microbes feed on this
A litre a day can be lost as sweat
Rate of heat loss 10x increased
Definition of hypothermia and causes
Core temperature less than 35 degrees
Or severe if under 28 degrees
Causes = behavioural (clothing, drinking too much), hypothyroidism and dermatological conditions such as eczema or psoriasis
Clinical features of hypothermia
- confusion
- coma
- cardiovascular collapse = hypotensive, arrhythmias + ventricular fibrillation
How is hypothermia treated
- ABC = airway, breathing and circulation maintained
- controlled warming at a rate of 2 degrees/hr
Or if severe cardiopulmonary bypass machine
Definition of hyperthermia and causes
Core temp higher than 38 degrees but is life threatening > 40 degrees
Causes =
exertional (running a marathon in high temp),
situational ( heat exhaustion),
as a side effects of drugs such as ecstasy or tranquillisers,
pyrexia
Clinical features of hyperthermia
Confusion
Seizures
Coma
Cardiovascular collapse
Causes of pyrexia
Infection
Blood transfusion/iatrogenic pyrogens
Inflammation (doesn’t have to be infectious, may be due to trauma or autoimmune conditions such as rheumatoid arthritis)
Malignancy
Hypothalamic insults ( damage to hypothalamus due to stroke, embolism, tumour or trauma)
The process of pyrogenesis
Due to mediators such as toxins, LPS and pyrogenic cytokines the pathway of arachidonic acid breakdown is initiated in which COX-2 (only in inflammatory states) produces PGE2 that crosses the BBB to alter the state of thermoregulation of hypothalamus and induce fever
When is fever bad
Head injury
Post cardiac arrest
Treatments for fever
(Investigate and treat the cause)
- paracetamol
- NSAIDS
- aspirin
- tepid sponging, cooling packs and ice
- exposure
- fan
- CPB
