Skin and Temperature Regulation

Question 1

What is the core body temperature of humans?

What happens above and below this temperature?

Answer 1

37 +/- 0.5 degrees

Above 41 degrees proteins start to denature

Below 30 degrees lose consciousness

Question 2

What does normal body temperature vary with?

Answer 2

External temperature
Activity
Circadian rhythm
Menstrual cycle

Question 3

Explain thermal balance

Answer 3

Core temperature is maintained by balancing heat loss and heat gain

Basal metabolic rate makes up the basis of heat production.

Heat is lost or gained by Radiation, Convection and Conduction

Heat is lost by evaporation

Question 4

Explain heat production

Answer 4

About 80 kcal/hr produced at rest

About 600 kcal/hr at a brisk walk would raise temp 1 degree per 10 mins

This needs to be compensated for or we would overheat

Question 5

Explain radiation

Answer 5

60% of heat loss
Just lost to atmosphere

Can also be a source of heat gain

Question 6

Explain evaporation

Answer 6

Evaporation = respiration + sweating

Lose about 600ml/day at rest

But 4L/hr at extremes (600kcal/l)

Question 7

Explain conduction

Answer 7

Conduction = heat transfer direct between touching objects

Can gain or lose heat

Question 8

Explain convection

Answer 8

Convection = “fluid” conduction hence wind chill and water chill

Important in blood too

Question 9

How do warm receptors respond to a rise in temperature?

Answer 9

Start off at base level

Increase in temperature causes a rapid increase in APs which then ease off to a higher base level than originally.

When temperature decreases the APs will briefly stop before continuing again and returning to a normal frequency

Question 10

How do cold receptors respond to a rise in temperature?

Answer 10

Start off at base level

Temperature rises and APs stop briefly before starting again (but still at a lower frequency than normal)

When temperature drops again the APs rise and then settle back to base level

Question 11

How do we detect body temperature?

Answer 11

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

Central thermoreceptors
-Loacted in spinal cord, abdominal organs, hypothalamus

Question 12

Where do peripheral and central thermoreceptors feed information into?

Answer 12

Hypothalamic thermoregulatory center

Question 13

Heat generated within the body in response to cold stress is increased by…

Answer 13

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 14

How does brown adipose generate heat?

Answer 14

Mitochondria uncouple proton pump gradient from ATP generation so that metabolism just produces heat

Question 15

How is heat loss from the body reduced during cold stress?

Answer 15

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

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

Question 16

What is hypothermia?

Answer 16

A fall in body temperature to below 35 degrees

Question 17

Who is at risk of hypothermia?

Answer 17

Neonates
Elderly
Vagrants
Cold stone workers
Outdoor pursuits
North Sea workers

Question 18

How are neonates at risk of hypothermia?

Answer 18

Big surface area to volume ratio
-core temperature close to surface

Not much fat

Dont shiver well
-motor control isnt fully developed

Do have brown adipose tissue though

Question 19

How are elderly at risk of hypothermia?

Answer 19

Do not detect temp change so well, less shivering capacity, more immobile

Question 20

How do you treat cold stress/ hypothermia?

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

Fast re-warming by immersion in water, extracorporeal circulation

Question 21

What are the two processes that cause frost bite?

Answer 21

Vascular

Cellular

Question 22

How do vascular cold stress complications cause frost bite?

Answer 22

• Vasoconstriction
• Increase in viscosity
• Promotes thrombosis
• Causes anoxia

Question 23

How do cellular cold stress complications cause frost bite?

Answer 23

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

Question 24

How big a problem is winter mortality?

Answer 24

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

Question 25

Heat loss within the body in response to heat stress is increased by…

Answer 25

Vasomotor control
-Arteriolar dilation incraeses 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 26

What is heat exhaustion?

Answer 26

(Heat illness)
-Body temperature raised in range 37.5-40 degrees

• 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

What is heat stroke?

Answer 27

(Heat injury)
-Body temperature raised above 40 degree

• Body’s temperature control mechanisms fail
• Symptoms include hot dry skin (sweating ceased) and circulatory collapse

Question 28

Who is most at risk from heat stress?

Answer 28

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

Question 29

What is the treatment for heat stress?

Answer 29

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

Question 30

What is fever?

Answer 30

Part of the body’s mechanism for fighting infection

Caused by endogenous pyrogens (IL-1, IL-6)

Question 31

What is your set point temperature

Answer 31

Concept of set point controlled by the hypothalamus.

When you exercise, sit in sun etc your core body temperature rises above your set point and you feel hot

Question 32

How is your set point temperature changed?

Answer 32

Endogenous pyrogens shift the set point

Caused by local production of prostaglandins by cycle-oxygenase in the hypothalamus

Explains why aspirin and paracetamol reduce fever

Question 33

How does set point relate to fever?

Answer 33

In exercise your core temperature rises above set point and you feel hot.

In fever your set point rises above your core temperature.
Your core temp increases to catch up but you still feel cold.

Therefore core temperature is raised but you feel cold so shiver and wrap in blankets etc

Question 34

What are the pros and cons of fever?

Answer 34

Body temperature regulates around a higher than normal body temperature

Part of the body’s mechanism for fighting infection.

Mild fever is beneficial
Severe fever is dangerous