Skin temperature and control

Question 1

Describe normal body temperature

Answer 1

• Man is homeothermic	
• Core body temp is normally 37 ± 0.5°C
• Above 41°C proteins start to denature
• Below 30°C lose consciousness
• Varies with
	○ external temp
	○ activity
	○ circadian rhythm
	○ menstrual cycle 
• Core temperature is maintained by balancing heat loss and heat gain

Question 2

How does the body maintain thermal balance?

Answer 2

• Convection: “fluid” conduction hence wind chill and water chill, important in blood too (the same as conduction but with air and water)
• Conduction: heat transfer direct between touching objects
• Evaporation: respiration and sweating (about 600ml/day at rest but 4L/hour at extremes loses 600 kcal/L)
• Radiation: 60% of heat loss can be a source of heat gain

Question 3

Where are the different types of thermoreceptors located?

Answer 3

• Peripheral thermoreceptors: skin, especially in face, scrotum
• Central thermoreceptors: spinal cord, abdominal organs, hypothalamus

Question 4

Describe the response to cold stress

Answer 4

Heat generated within the body is increased by:

• 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, only significant in infants, due to brown adipose tissue

Heat loss from the body is reduced by:

• Vasomotor control: sympathetic arteriolar constriction reduces delivery of blood to the skin
• Behavioural responses: reducing surface area, adding clothing, moving to warmer environment

Question 5

Who is most at risk of hypothermia?

Answer 5

• neonates: big SA:volume, not much fat, don’t shiver well, but do have BAT
• elderly: do not detect temp change so well, less shivering capacity, more immobile
• vagrants
• cold store workers
• outdoor pursuits
• North Sea workers

Question 6

What is the treatment of hypothermia?

Answer 6

• dry/insulate to prevent further heat loss
• slow rewarming with bag/blankets
• internal rewarming with hot drinks and/or warm air
• fast re-warming by immersion in water, extracorporeal circulation

Question 7

What happens in frostbite?

Answer 7

• Vascular 
	○ vasoconstriction
	○ increase in viscosity
	○ promotes thrombosis
	○ causes anoxia
• Cellular
	○ ice crystals form in extracellular space
	○ increases extracellular osmolality
	○ causes movement of water from intracellular space
	○ cell dehydration and death

Question 8

Describe winter mortality

Answer 8

• 40% excess mortality in winter in UK
• partly due to increases in heart attacks and strokes following periods of cold weather
• increased vasoconstriction and increased blood viscosity contribute

Question 9

Describe the body’s response to heat stress

Answer 9

Heat production is minimised by:

• Decreased physical activity
• Decreased food intake

Heat loss from the body is increased by:

• Vasomotor control: arteriolar dilation increased 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

Question 10

What is heat exhaustion?

Answer 10

• body temperature raised in range 37.5-40ºC
• results in vasodilation and drop in central blood volume
• caused by a disturbance of the body’s fluid/salt balance due to excessive sweating
• symptoms include headache, confusion, nausea, profuse sweating, clammy skin, tachycardia, hypotension, weak pulse, fainting & collapse

Question 11

What is heat stroke?

Answer 11

• body temperature raised above 40ºC
• body’s temperature control mechanisms fail
• symptoms include hot dry skin (sweating ceased) & circulatory collapse

Question 12

Who is most at risk of heat exhaustion or heat stroke?

Answer 12

• neonates & the elderly
• people doing physical work in hot humid environments
• workers wearing non-breathable protective clothing

Question 13

What is the treatment of heat stroke or heat exhaustion?

Answer 13

• move to cool environment
• remove clothing
• fan
• sponge with tepid water
• give fluids (oral, intravenous)

Question 14

Explain fever

Answer 14

• Part of the body’s mechanism for fighting infection
• Caused by endogenous pyrogens (IL-1, IL-6)
• Concept of ‘set point’ controlled by the hypothalamus
  * endogenous pyrogens shift the set point
  * caused by local production of prostaglandins by cyclooxygenase in the hypothalamus
  * explains why aspirin & 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
• Severe fever is dangerous