Physiology: Skin & Temp Regulation

Question 1

Normal body temperature:
Varies with:
_
_
_
_
Humans are: homeo...

Answer 1

Humans are 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

Thermal Balance

Answer 2

Heat production -->
Convection +/-
Conduction +/-
Evaporation -
Radiation +/-

Question 3

Body Heat production

Answer 3

~ 80 kcal/hr at rest
~ 600 kcal/hr at a brisk walk
would raise temp by 10C per 10 min

Question 4

Convection

Answer 4

= “fluid” conduction
hence wind chill &
water chill
Important in blood too

Question 5

Conduction

Answer 5

= heat transfer direct
between touching
objects

Question 6

Evaporation

Answer 6

= respiration + sweating
~600ml/day at rest
But 4l/hour at extremes
loses 600kcal/l

Question 7

Radiation

Answer 7

~ 60% of heat loss

Can be source of heat gain

Question 8

Detection of body temperature: cold/warm

Answer 8

“Cold” receptors and “warm” receptors

Question 9

Cold Pain

Heat Pain

Answer 9

Cold Pain –> Cold Receptors

Warmth Receptors –> Heat Pain

Question 10

Detection of body temperature: p/c

Answer 10

Peripheral thermoreceptors
located in the skin, especially in face, scrotum

Central thermoreceptors
located in spinal cord, abdominal organs, hypothalamus

Question 11

Warm Receptor - detection

Answer 11

increases frequency of signals during warm phase

reduced in cold phase

Question 12

Cold Receptor - detection

Answer 12

increases frequency of signals during cold phase

reduced in hot phase

Question 13

Change in environmental temperature —>

Answer 13

• –> peripheral thermoreceptors
• -> Hypothalamic thermoregulatory centre
• resposes to changes in temp

Question 14

Change in core body temperature —>

Answer 14

• –> central thermoreceptors
• -> Hypothalamic thermoregulatory centre
• resposes to changes in temp

Question 15

Response to cold stress

Heat generated within the body is increased by:

Answer 15

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

Question 16

Response to cold stress

Heat loss from the body is reduced by:

Answer 16

Vasomotor control:
- sympathetic arteriolar constriction reduces delivery of blood to the skin

Behavioural responses:
- reducing surface area, adding clothing, moving to warmer environment

Question 17

Complications of Cold Stress

& Who is at risk?

Answer 17

Hypothermia
a fall in deep body temperature to below 35ºC
Those at risk
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
North Sea workers
outdoor pursuits

Question 18

Cold StressTreatment

Answer 18

Treatment
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

Question 19

Vascular & Cellular response to Cold Stress condition:

Answer 19

Frost bite
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 20

Winter mortality &

Cold stress

Answer 20

Winter mortality
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 21

Response to heat stress

Answer 21

Heat production is minimised by:

Decreased physical activity

Decreased food intake

Heat loss from the body is increased by:

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

Question 22

Complications of heat stress
1.
2.

Answer 22

Heat exhaustion (heat illness)
Heat stroke (heat injury)

Question 23

Heat exhaustion (heat illness)

Answer 23

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, weak pulse, hypotension, tachycardia, fainting & collapse

Question 24

Heat stroke (heat injury)

Answer 24

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

Question 25

Who is most at risk of heat stress?

Answer 25

Those most at risk
neonates & the elderly
people doing physical work in hot humid environments
workers wearing non-breathable protective clothing

Question 26

Treatment of heat stress

Answer 26

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

Question 27

Fever

Answer 27

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 cyclo-oxygenase 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