Skin and Temperature Regulation Flashcards
What does homeothermic mean?
Maintains stable internal body temperature regardless of external influence
What is normal core body temperature?
37 +/- 0.5oC
At what temperature do proteins start to denature?
41oC
At what temperature do you lose consciousness?
Below 30oC
What does core body temperature vary with?
- External temp
- Activity
- Circadian rhythm
- Menstrual cycle
How is core body temperature maintained?
By balancing heat loss and heat gain
What are the different methods that thermal balance is achieved?
Convection
Conduction
Evaporation
Radiation
Heat production
What is evaporation in terms of thermal balance?
Respiration and sweating
About 600ml/day at rest
But 4L/hour at extremes and losses 600kcal/L
What is conduction in terms of thermal balance?
Heat transfer direct between touching objects
What is convection in terms of thermal balance?
Fluid conduction hence wind chill and water chill
Important in blood too
How is body temperature detected?
Cold and warm thermoreceptors
What are thermoreceptors divided into?
- Peripheral thermoreceptors
- Located in the skin, especially in face and scrotum
- Central thermoreceptors
- Located in spinal cord, abdominal organs and hypothalamus
Where are peripheral thermoreceptors located?
Skin, especially in face and scrotum
Where are central thermoreceptors located?
Spinal cord, abdominal organs and hypothalamus
How does an increases in temperature impact a warm receptor, and a decrease in temperature impact a cold receptor?
Increases frequency
Where do peripheral and central thermoreceptors feed their sensory information into?
Hypothalamic thermoregulatory centre
What do peripheral receptors detect?
Change in environmental temperature
What do central receptors detect?
Change in core body temperature
What are different ways that heat is generated within the body in response to cold stress?
- General metabolism
- Oxidative phosphorylation and other chemical reactions are not 100% efficient
- Voluntary muscular activity
- “Futile” muscular activity
- Shivering thermogenesis
- Involuntary muscular activity
- Nonshivering thermogenesis
- In humans is only significant in infants, due to brown adipose tissue
How does general metabolism generate heat?
- Oxidative phosphorylation and other chemical reactions are not 100% efficient
For generating heat, what is voluntary muscular activity described as?
- “Futile” muscular activity
What is shivering thermogenesis?
- Involuntary muscular activity
In what age group is non-shivering thermogenesis significant in?
Infants due to brown adipose tissue
How is heat loss from the body reduced?
- Vasomotor control
- Sympathetic arteriolar constriction reduces delivery of blood to the skin
- Behavioural responses
- Reducing surface area, adding clothing, moving to warmer environment
How does vasomotor control reduce heat loss?
- Sympathetic arteriolar constriction reduces delivery of blood to the skin
What are some illnesses caused by cold stress?
- Hypothermia
- Frost bite
When does hypothermia occur?
Is a fall in deep body temperature below 35
Who is most at risk of hypothermia?
- Neonates
- Big SA:volume, not much fat, don’t shiver well, but do have brown adipose tissue (BAT)
- Elderly
- Do not detect temperature change so well, less shivering capacity, more immobile
- Vagrants
- Cold store workers
- Outdoor pursuits
- North sea workers
Why are neonates at risk of hypothermia?
- Big SA:volume, not much fat, don’t shiver well, but do have brown adipose tissue (BAT)
What does BAT stand for?
Brown adipose tissue
Why are the elderly at risk of hypothermia?
- Do not detect temperature change so well, less shivering capacity, more immobile
What is the treatment of hypothermia?
- Dry/insulate to prevent further heat loss
- Slow re-warming with bag/blankets
- Internal re-warming with hot drinks and/or warm air
- Fast re-warming by immersion in water, extracorporeal circulation
What is frostbite?
Injury caused by freezing of the skin and underlying tissues
What kinds of changes does frost bite cause?
Vascular changes:
- Vasoconstriction
- Increase in viscosity
- Promotes thrombosis
- Causes anoxia (an absence of oxygen)
Cellular changes:
- Ice crystals form in extracellular space
- Increases extracellular osmolarity
- Causes movement of water from intracellular space
- Cell death and dehydration
What are some vascular changes due to frost bite?
- Vasoconstriction
- Increase in viscosity
- Promotes thrombosis
- Causes anoxia (an absence of oxygen)
What are some cellular changes due to frostbite?
- Ice crystals form in extracellular space
- Increases extracellular osmolarity
- Causes movement of water from intracellular space
- Cell death and dehydration
How does mortality change in winter?
40% excess mortality in winter in UK
Why does mortality increases in the winter?
- Partly due to increase in heart attacks and strokes following periods of cold weather
- Increased vasoconstriction and increased blood viscosity contribute
How is heat production minimised in response to heat stress?
- Decreased physical activity
- Decreased foot intake
How is heat loss from the body increased in response to heat stress?
- Vasomotor control
- Arteriolar dilation increases delivery of blood to the skin
- Sweating
- Sympathetic cholinergic fibres increase evaporative heat loss
- Behavioural responses
- Increasing surface area, removing clothing, moving to shaded area
How does vasomotor control increase heat loss?
- Arteriolar dilation increases delivery of blood to the skin
How does sweating increase heat loss?
- Sympathetic cholinergic fibres increase evaporative heat loss
How do behaviour reponses increase heat loss?
- Increasing surface area, removing clothing, moving to shaded area
What are some illnesses due to heat stress?
- Heat exhaustion (heat illness)
- Heat stroke (heat injury)
Who are some people at risk of heat stress?
- Neonates
- Elderly
- People doing physical work in hot 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
- Give fluids (oral, IV)
When does heat exhaustion occur?
Body temperature raised in range of 37.5-40
What changes in the body does heat exhaustion cause?
Results in vasodilation and drop in central blood volume
Caused by disturbance of the body’s fluid/salt balance due to excessive sweating
What is the clinical presentation of heat exhaustion?
- Headache
- Confusion
- Nausea
- Profuse sweating
- Clammy sin
- Tachycardia
- Hypotension
- Weak pulse
- Fainting and collapse
When does heat stroke occur?
Body temperature raised above 40
What causes heat stroke?
Body’s temperature control mechanism fails
What is the clinical presentation of heat stroke?
- Hot dry skin (sweating ceased)
- Circulatory collapse
What is a fever?
Part of body’s mechanism for fighting infection, caused by endogenous pyrogens (IL-1, IL-6)
What is a fever caused by?
Endogenous pyrogens (IL-1, IL-6)
Explain the concept of ‘set point’ controlled by 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
- Analogy of a thermostat that has been reset, body temperature regulates around a higher than normal body temperature
- Mild fever is beneficial, sever fever is dangerous
Are fevers beneficial?
- Mild fever is beneficial, sever fever is dangerous
What is changing of the set point during a fever caused by?
- Caused by local production of prostaglandins by cyclo-oxygenase in hypothalamus
