Extreme Cold Flashcards
What acute thermoeffector RESPONSES occur to the cold?
Constriction of peripheral blood vessels to prevent heat dissipation,
Increased energy metabolism and shivering,
And hormonal output eg. Adrenaline, to maintain internL heat production
What mechanism occurs to produce the responses to cold?
Cold signals are transduced through TRPM8 ( a receptor),
This travels along dorsal root ganglion sensory neurons and trigeminal ganglion sensory neurons
This increases metabolic heat production and vasoconstriction
What acute changes occur when exercising in the cold?
Rectal and skin temp decreases, O2 consumption increases, Oxyhaemoglobin curve shifts left, so decreased release and extraction of O2 at muscles, Decrease in plasma volume, So decrease in O2 transport,
Why might an athlete exercising in the cold experience a decrease in plasma volume?
Because Central blood volume increases to maintain internal heat production, which stimulates baroreceptor inhibiton of vasopressin secretion leading to low blood volume, diuresis and hemoconcentration
Remember: sub max exercise in the cold means working at higher thresholds earlier and VO2 is higher at LT because increase in metabolic rate due to decreased core temp
Remember
How else might exercise in the cold be problematic?
Mechanical efficiency reduced by muscle chilling and dehydration, Movement opposed by shivering, Muscle perfusion decreased, Weight of heavy clothing, Law of Arrhenius, Cost of moving over ice and snow
What are catecholamines?
Hormones released from the adrenal glands during stress eg. Adrenaline, noradrenaline, corticoids,
How does the catecholamine response to cold stress work?
The cold stress stimulates sympathoadrenal secretion, then the activation of adrenoreceptors leads to catecholamine stimulation of lipolysis, hepatic glycogenolysis and gluconeogenesis
What is sympathoadrenal secretion?
The connection between the sympathetic NS and adrenal medulla
How does the hypothalamus activate the adrenal cortex vs. Adrenal medulla?
Adrenal cortex- Via hormonal signals
Adrenal medulla - via nerve impulses
What happens to nerve conduction velocity when temp decreases?
Na channel gating is slowed, leading to slowing of sodium influx for depolarisation of axon all membrane and therefore the nerve conduction velocity decreases
How does frostbite develop?
Freezing of tissues -> ice crystal form -> cell dehydration -> frostbite
Local vasoconstriction, increased blood viscosity -> reduces blood flow -> hypoxia, blood clot -> local metabolic acidosis -> frostbite
What areas of the body are susceptible to peripheral cold induced Vasoconstriction?
Acral skin regions like nose, toes, fingers
What is the hunting reaction?
CIVC occurs in acral skin regions to reduce heat loss -> then approx 5-10 mins after the start of cold exposure, the blood vessels in these areas vasodilate -> CIVD increases blood flow and temp to prevent injuries
Does water or air have a larger thermal conductivity?
Water, heat loss occurs 4x faster
What part of our body has the highest thermal resistivity?
Fat
What physiological adjustments might occur as a result of chronic cold exposure?
Habituation - blunted shivering and cutaneous vasoconstriction
Metabolic acclimatisation - enhanced shivering and non-shivering thermogenesis
Insulative acclimatisation - enhances cutaneous vasoconstriction, improves muscle blood flow to subcutaneous shell
