Skin and Temperature Control Flashcards
Describe normal body temperature
Homeothermic
Core temp. is 37C + 0.5C
Above 41 then proteins denature
Below 30 then lose consciousness
Managed by balancing heat loss and heat gain
What does normal body temp. vary with?
External temperature
Activity
Circadian rhythm
Menstrual cycle
What is included in thermal balance?
Convection, conduction, radiation and evaporation
What is normal heat production at rest?
80kcal/h at rest
600kcal/h at brisk walk which would raise temp. by 1C per 10 mins if no thermal balance
What is conduction?
Heat transfer direct between touching objects
What is convection?
Fluid conduction hence wind chill and water chill
Important in blood too
What is evaporation in thermal balance?
Respiration and sweating - 600ml a day at rest
But 4l/ hr at extremes looses 600kcal/l
What is radiation in thermal balance?
60% of heat loss
Can be source of heat gain
Where are peripheral thermoreceptors located?
In skin, especially the face and scrotum
Where are central thermoreceptors located?
In spinal cord, abdominal organs and hypothalamus
How is body temperature detected?
Warm and cold receptors
Have different time and amplitude of firing of APs
What influences peripheral thermoreceptors?
Change in environmental temperature
What influences central thermoreceptors?
Change in core body temperature
How is heat generated in the body increased by?
General metabolism - oxidative phosphorylation and other chemical reactions
Voluntary muscular activity - futile muscular activity
Shivering thermogenesis - involuntary muscular activity
Non-shivering thermogenesis - only in infants as brown adipose tissue
How can heat loss in the body be reduced?
Vasomotor control - sympathetic arteriolar constriction reduces delivery of blood to skin
Behavioural responses - adding clothing, moving to warmer environment and reducing surface area
What is the response to cold stress?
Hypothermia - a fall in body temp. to below 35C
Who is at risk of hypothermia?
Neonates
Elderly
Homeless people
Cold store workers
Outdoor pursuits
What is the treatment of cold stress?
Dry/ insulate to prevent further heat loss
Slow re-warming with bag/ blankets
Internal re-warming with hot drinks and/ or warm air
Rapid re-warming with immersion in water and extracorporeal circulation
What are the consequences of cold stress?
Frost bite
Vascular - vasoconstriction, increase in viscosity, promotes thrombosis and causes anoxia
Cellular - ice crystals form in extracellular space, increase in extracellular osmolarity and causes cell dehydration and death
Describe winter mortality by cold stress
40% excess mortality in winter in UK
Increases in MIs and strokes following periods of cold weather
Increased vasoconstriction and increased blood viscosity contribute
What is heat production minimised by?
Decreased physical activity and decreased food intake
How is heat loss from the body increased by?
Vasomotor control - arteriolar dilatation
Sweating - sympathetic cholinergic fibres increase evaporation heat loss
Behavioural - remove clothing, moving to shaded area and increasing surface area
What is heat exhaustion (heat illness)?
Body temp. raised in range 37.5-40C
Results in vasodilation and drop in central blood volume
Caused by disturbance in body’s fluid/ salt balance due to excessive sweating
What are the symptoms of heat exhaustion?
Headache, confusion, nausea, profuse sweating, clammy skin, tachycardia, hypotension, weak pulse, fainting and collapse
What is heat stroke (heat injury)?
Body temp. is raised above 40C
Body’s temp. control mechanisms have failed
What are the symptoms of heat stroke?
Hot dry skin (sweating has stopped) and circulatory collapse
Who are most at risk of heat stress?
Neonates and the elderly
People doing physical work in hot and humid environments
Workers wearing non-breathable protective clothing
What is the treatment for heat stress?
Move to cool environment, remove clothing, fan, sponge with tepid water and give fluids
Describe fever
Part of body’s mechanism of fighting infection
Caused by endogenous pyrogens
Concept of set point controlled by hypothalamus
What is the concept of set point set by the hypothalamus?
Endogenous pyrogens shift the set point
Caused by local production of prostaglandins by cyclo-oxygenase in hypothalamus
Explains why aspirin and paracetamol reduce fever
What is the difference between exercise and fever with increased temp.?
Exercise increased core temp. above the set temp.
Fever is increased set temp. by pyrogens which increases core temp.
