Skin and Temperature Control

Question 1

Describe normal body temperature

Answer 1

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

Question 2

What does normal body temp. vary with?

Answer 2

External temperature
Activity
Circadian rhythm
Menstrual cycle

Question 3

What is included in thermal balance?

Answer 3

Convection, conduction, radiation and evaporation

Question 4

What is normal heat production at rest?

Answer 4

80kcal/h at rest
600kcal/h at brisk walk which would raise temp. by 1C per 10 mins if no thermal balance

Question 5

What is conduction?

Answer 5

Heat transfer direct between touching objects

Question 6

What is convection?

Answer 6

Fluid conduction hence wind chill and water chill
Important in blood too

Question 7

What is evaporation in thermal balance?

Answer 7

Respiration and sweating - 600ml a day at rest
But 4l/ hr at extremes looses 600kcal/l

Question 8

What is radiation in thermal balance?

Answer 8

60% of heat loss
Can be source of heat gain

Question 9

Where are peripheral thermoreceptors located?

Answer 9

In skin, especially the face and scrotum

Question 10

Where are central thermoreceptors located?

Answer 10

In spinal cord, abdominal organs and hypothalamus

Question 11

How is body temperature detected?

Answer 11

Warm and cold receptors
Have different time and amplitude of firing of APs

Question 12

What influences peripheral thermoreceptors?

Answer 12

Change in environmental temperature

Question 13

What influences central thermoreceptors?

Answer 13

Change in core body temperature

Question 14

How is heat generated in the body increased by?

Answer 14

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

Question 15

How can heat loss in the body be reduced?

Answer 15

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

Question 16

What is the response to cold stress?

Answer 16

Hypothermia - a fall in body temp. to below 35C

Question 17

Who is at risk of hypothermia?

Answer 17

Neonates
Elderly
Homeless people
Cold store workers
Outdoor pursuits

Question 18

What is the treatment of cold stress?

Answer 18

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

Question 19

What are the consequences of cold stress?

Answer 19

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

Question 20

Describe winter mortality by cold stress

Answer 20

40% excess mortality in winter in UK
Increases in MIs and strokes following periods of cold weather
Increased vasoconstriction and increased blood viscosity contribute

Question 21

What is heat production minimised by?

Answer 21

Decreased physical activity and decreased food intake

Question 22

How is heat loss from the body increased by?

Answer 22

Vasomotor control - arteriolar dilatation
Sweating - sympathetic cholinergic fibres increase evaporation heat loss
Behavioural - remove clothing, moving to shaded area and increasing surface area

Question 23

What is heat exhaustion (heat illness)?

Answer 23

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

Question 24

What are the symptoms of heat exhaustion?

Answer 24

Headache, confusion, nausea, profuse sweating, clammy skin, tachycardia, hypotension, weak pulse, fainting and collapse

Question 25

What is heat stroke (heat injury)?

Answer 25

Body temp. is raised above 40C
Body’s temp. control mechanisms have failed

Question 26

What are the symptoms of heat stroke?

Answer 26

Hot dry skin (sweating has stopped) and circulatory collapse

Question 27

Who are most at risk of heat stress?

Answer 27

Neonates and the elderly
People doing physical work in hot and humid environments
Workers wearing non-breathable protective clothing

Question 28

What is the treatment for heat stress?

Answer 28

Move to cool environment, remove clothing, fan, sponge with tepid water and give fluids

Question 29

Describe fever

Answer 29

Part of body’s mechanism of fighting infection
Caused by endogenous pyrogens
Concept of set point controlled by hypothalamus

Question 30

What is the concept of set point set by the hypothalamus?

Answer 30

Endogenous pyrogens shift the set point
Caused by local production of prostaglandins by cyclo-oxygenase in hypothalamus
Explains why aspirin and paracetamol reduce fever

Question 31

What is the difference between exercise and fever with increased temp.?

Answer 31

Exercise increased core temp. above the set temp.
Fever is increased set temp. by pyrogens which increases core temp.