The cold environment Flashcards
thermal neutral zone
- endotherms temperature tolerance zone
- maintain just heat movement across the skin 28-31 degrees if it gets warmer u rely on evaporation of sweat, lower than rely on increase metabolic rate and shivering
- in water much lower range 34.5 - 35.5 (harder for evaporation to work)
the core temp:
- vary in regards to environment temperature
- core region changes, small the colder outside (heart lungs and brain)
2 regions of skin
apical and nonapical
apical skin
around the ears, face, nose, hands & feet
- have arteriovenous anastomosis (glomus body) blood pathway to loose and increase heat loss
- sympathetic control of blood vessels, activation of sympathetic nervous system = vasoconstriction (no dilation control just constriction)
non-apical skin
- majority of skin
- sympathetic activity (vasoconstriction)
- sympathetic vasodilator activity (cholinergic –> Bradykinin–> vasodilation effect)
arrhythmias :
irregular heart beat
water specific heat per unit volume
~4000X greater than air
water thermal conductivity
~25X greater than air
convective heat transfer in water compared to air
~100 times higher
even in freezing water takes ___ to die from hypothermia
30 mins, before core temperature
__% of open water deaths within first few minutes of entering water
~55%
~60% of deaths are within 3 metres of safety
`67% are ‘good’ swimmers–> SO MOST DEATHS ARENT DUE TO HYPOTHERMIA
4 phases associated with cold water immersion:
Initial response to immersion (0-3 min)
Short-term immersion (3-15 min)
Long-term immersion (>30 min)
Post immersion (afterdrop)
Initial response to immersion: 0-3min CARDIOVASCULAR EFFECTS
- rapid tachycardia within seconds (colder the water the bigger the tachycardia)
- peripheral vacosinstriction and reduction in peripheral blood flow. increase in arteriole pressure
- in healthy people these strain on CV system minor risk but greater risk in cases of hypertension or CHD
tachycardia =
rapid HR
Initial response to immersion: 0-3min RESPIRATORY RESPONSES
- threat
- inspiratory gasp followed by uncontrollable hyperventilation
- 4X increase in ventilation during first minute of immersion
- fall in end-tidal and arteriole CO2 levels leaves to alkalosis and hypocapnia
- changes to ventricular fibrillation
- cerebal hypoxia
- left shift in Oxygen/Hb curve (O2 bound to haemoglobin more tightly)
- tetany, disorientation & clouding of consciousness
- feeling of dyspnoea (struggling breathing) continues for 3 mins reduction in breath holding ability
- you then adapt
Initial response to immersion: 0-3min METABOLIC RESPONSES
- rapid increase in metabolic rate
- increased CO2 production may counteract hypocapnia. but there is increase load on heart leading to risk of cardiac irregularities
Initial response to immersion: 0-3min HORMONAL REPSPONE
- evidence not conclusive
- some evidence for increases in plasma noradrenaline and adrenaline
- noradrenaline linked to activation of sympathetic nervous system
cold response mechanism: response if initiated by __
activation receptors in the skin that are stimulated by cold conditions
-thermosensitive mechanoreceptors, thermal nociceptors and cold receptors
cold receptors are located
in the superficial layers above subcutaneous fat
underpins rapid nature of response
cold response respiratory effects mechanisms:
- direct stimulation of respiratory centre by thermoafferents linked to peripheral cold receptors.
- may also be stimulation of pathways stimulating inspiratory muscles
cold response cardiovascular effects mechanisms:
predominantly linked to sympathetic activation
cold response metabolic effects mechanisms:
linked to increased muscle tension, increased activity of respiratory muscles
diving reflex: wheres it found
-homeostatic mechanism observed in air breathing vertebrates
diving reflex: type of mechanism
protective; activated by exposure of cold thermoreceptors in the face to water
diving reflex results:
pronounced bradycardia (slowing of heart) and suppression of expiratory pathways (driven by activation of parasympathetic pathways) -peripheral vasoconstriction --> sympathetic mechanism
diving reflex: Overall effect
redues oxygen delivery to non essential areas allow extended survival or extended diving times
The after drop:
people recovered from cold water immersion, they appear to be responsive and recovering well but then suddenly die due to cardia arrhythmia (irregular HB)
mechanism of after drop:
convective; cold blood from extremities reaching core but some research suggest its conductive