Skin and temperature control

Question 1

what is a humans core body temperature?

Answer 1

Core body temperature is normally 37 ± 0.5°C

Question 2

what happens in temperatures above 41C?

Answer 2

above 41°C proteins start to denature

Question 3

what happens below 30°C?

Answer 3

lose consciousnes

Question 4

what does normal body temperature slightly vary with?

Answer 4

external temperature
Activity
Circadian rhythm
Menstrual cycle

Question 5

what is core temperature maintained by?

Answer 5

balancing heat loss and heat gain

Question 6

what is convection?

Answer 6

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

Question 7

what is conduction?

Answer 7

heat transfer direct
between touching objects

Question 8

heat production of the body?

Answer 8

~ 80 kcal/h at rest
~ 600 kcal/h at a brisk walk
would raise temp by 1 0C per 10 min

Question 9

what role does radiation have on thermal balance?

Answer 9

60% of heat loss
Can be source of heat gain

Question 10

what role does evaporation have on thermal balance?

Answer 10

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

Question 11

how is body temperature detected?

Answer 11

Question 12

what are peripheral thermoreceptors?

Answer 12

Located in the skin, especially in face, scrotum

Question 13

what are central thermoreceptors?

Answer 13

Located in spinal cord, abdominal organs, hypothalamus

Question 14

what effect does increased temperature/amplitude have on warm and cold receptors?

Answer 14

Question 15

describe the mechanism of detection of body temperature?

Answer 15

Question 16

how is heat generation within the body increased?

Answer 16

General metabolism:
Oxidative phosphorylation and other chemical reactions are not 100% efficient

Voluntary muscular activity
“futile” muscular activity

Shivering thermogenesis
Involuntary muscular activity

Non-shivering thermogenesis
Only significant in infants due to brown adipose tissue

Question 17

how is heat loss from the body reduced by?

Answer 17

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

Behavioural responses
Adding clothing, moving to warmer environment, reducing surface area

Question 18

what is hypothermia?

Answer 18

A fall in deep body temperature to below 35 ºC

Question 19

who is at risk to cold stress?

Answer 19

Neonates (big SA:volume, not much fat, do not shiver well, but do have BAT)
Elderly (do not detect temp change so well, less shivering capacity, more immobile
Homeless people
Cold store workers
Outdoor pursuits

Question 20

how is cold stress treated?

Answer 20

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 by immersion in water, extracorporeal circulation

Question 21

what are vascular consequences of cold stress?

Answer 21

Vasoconstriction
Increase in viscosity
Promotes thrombosis
Causes anoxia

Question 22

what are cellular causes of cold stress?

Answer 22

Ice crystals form in extracellular space
Increases extracellular osmolality
Causes movement of water from intracellular space
Cell dehydration and death

Question 23

what is winter mortality?

Answer 23

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

Question 24

what is heat production minimized by?

Answer 24

Decreased physical activity

Decreased food intake

Question 25

what is heat loss from the body increased by?

Answer 25

Vasomotor control
Arteriolar dilation increases delivery of blood to the skin

Sweating
Sympathetic cholinergic fibres increase evaporative heat loss

Behavioural responses
Removing clothing, moving to shaded area, increasing surface area

Question 26

when does heat exhaustion occur?

Answer 26

Body temperature raised in range 37.5-40 ºC
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 and collapse

Question 27

when does heat stroke occur?

Answer 27

Body temperature raised above 40 ºC
Body’s temperature control mechanisms fail
Symptoms include hot dry skin (sweating stops) and circulatory collapse

Question 28

who is most at risk of heat stress?

Answer 28

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

Question 29

how is heat stress treated?

Answer 29

Move to cool environment
Remove clothing
Fan
Sponge with tepid water
Give fluids (oral, intravenous)

Question 30

what is a fever?

Answer 30

Part of the body’s mechanism for fighting infection
Caused by endogenous pyrogens (IL-1, IL-6)

Question 31

Concept of ‘set point’ controlled by the hypothalamus?

Answer 31

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