Thermoregulation

Question 1

What is core body temperature?

Why do we thermoregulate?

Answer 1

•Core body temp is normally 37 ± 0.5°C

Humans are HOMEOTHERMIC so we have a tight window in which we need to keep our core temperature to function properly.

Question 2

What does body temperature vary with?

Answer 2

External temperature

Activity

Circadian rhythm

Menstrual cycle

Question 3

4 methods of heat loss and gain?

Answer 3

• Radiation (60% of heat lost via this method. Can also gain heat eg lying in sun all day)
• Evaporation (sweat and respiration)
• Conduction (heat gain or loss via direct contact eg sitting on cold bench will chill you)
• Convection

Question 4

What detects body temperature?

Answer 4

Cold and warm receptors

Can be CENTRAL and PERIPHERAL

Question 5

Where are the peripheral thermoreceptors and the central thermoreceptors?

Answer 5

Peripheral = SKIN especially face and scrotum

Central = Abdominal organs, spinal cord and hypothalamus

Question 6

What source of temperature do the peripheral and central chemoreceptors detect?

Answer 6

Peripheral chemoreceptors: Change in environmental temperature

Central chemoreceptors: Change in core body temperature

Question 7

What do the peripheral and central chemoreceptors feed into?

Answer 7

Hypothalamic thermoregulatory centre

Question 8

In response to cold - how is heat generated by the body increased?

Answer 8

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 9

How do we reduce heat loss in response to cold stress?

Answer 9

Vasomotor control

sympathetic arteriolar constriction reduces delivery of blood to the skin

Behavioural responses

reducing surface area, adding clothing, moving to warmer environment

Question 10

What is hypothermia defined as?

Answer 10

A fall in deep body temperature to below 35 degrees

Question 11

Who is at risk of hypthermia?

Answer 11

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 - people living in the outdoors

cold store workers

outdoor pursuits

North Sea workers

Question 12

What is the treatment for hypothermia?

Answer 12

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 – peripheral vasodilation – less blood in the heart – can cause heart attack

Question 13

What happens if cold stress is not resolved?

Answer 13

Progresses to FROST BITE

Question 14

Frost Bite involves both X and Y mechanisms…

Answer 14

X = VASCULAR

Y = CELLULAR

Question 15

What is the vascular response to cold stress (frost bite)

Answer 15

vasoconstriction

increase in viscosity

promotes thrombosis

causes anoxia

Question 16

What is the cellular response to cold stress (frost bite)

Answer 16

ice crystals form in extracellular space

increases extracellular osmolality

causes movement of water from intracellular space

cell dehydration and death

Question 17

Cold Stress accounts for X% excess death rates in winter?

WHY?

Answer 17

40%

Increased VC and viscosity of blood due to cold weather leads to increased strokes and MIs

Question 18

In response to heat stress, how is heat production minimised?

Answer 18

Decreased physical activity and decreased food intake

Question 19

How is heat loss from the body maximised during reponse to heat stress?

Answer 19

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 20

What body temperature is associated with heat exhaustion?

Answer 20

Body temperature raised in a range (37.5 - 40) degrees celcius

Question 21

What is the physiological response to heat exhaustion?

Answer 21

Vasodilation and resultant drop in blood volume

Body’s fluid / salt regulation is disturbed as a result of excessive sweating

Question 22

What are the symptoms of heat exhaustion?

Answer 22

headache, confusion, nausea, profuse sweating, clammy skin, tachycardia, hypotension, weak pulse, fainting & collapse

Question 23

What temperatures are assocaited with heat stroke?

Answer 23

Body temperature raised above 40 degrees

body’s temperature control mechanisms fail

Question 24

What are the symptoms of heat stroke?

Answer 24

symptoms include hot dry skin (sweating ceased) & circulatory collapse

Question 25

Who is at the most risk to heat stroke?

Answer 25

neonates & the elderly

people doing physical work in hot humid environments

workers wearing non-breathable protective clothing

Question 26

What is the treatment for heat stroke?

Answer 26

move to cool environment

remove clothing

fan

sponge with tepid water

give fluids (oral, intravenous)

Question 27

What causes fever?

Answer 27

Part of the body’s mechanism for fighting infection

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

Question 28

What controls the ‘set point’ for temperature control?

Answer 28

Hypothalamus

Question 29

How does a fever raise body temperature?

Answer 29

Prostaglandins have effect on endogenous pyrogens which shift the set point…

Aspirin & paracetamol reduce fever because they inhibit prostaglandins.

Question 30

Describe set point and core body temp with relation to

a) exercise
b) fever

Answer 30

a) In exercise your core body temp is higher than the set point and so you heat up and sweat
b) In fever your set point is above your core body temp so your body starts off cold and ends up very warm

Mild fever is beneficial but severe fever can be dangerous