L6. Physiological responses to heat and cold stress Flashcards
What are the main mechanisms of heat transfer in humans?
Convection, radiation, conduction, and evaporation
What is the primary mechanism for heat loss in humans during high temperatures?
Evaporation of sweat
How does the pre-optic anterior hypothalamus regulate temperature?
It integrates signals from various thermoreceptors to produce effector responses
What is the role of TRPV3 ion channels in thermoregulation?
They drive warm afferent signals
What is the significance of mean body temperature in thermoregulation?
It determines physiological responses to heat and cold stress
What happens to cardiac output during hyperthermia?
It increases, primarily driven by heart rate
What is the functional importance of increasing skin blood flow during heat stress?
It enhances convective and evaporative heat loss
What are the three main pathways through which heat stress can cause mortality?
Cardiovascular collapse, splanchnic hypoperfusion, and microbial translocation
How does skin temperature affect the onset of sweating?
Higher skin temperatures lower the core temperature threshold for sweating
What is the impact of dehydration on thermoregulation?
It exacerbates cardiovascular strain and reduces sweat efficiency
What is core temperature typically at rest?
Between 36.5°C and 37.5°C
At what core temperature does protein misfolding and cell death occur?
Around 42°C
What is the role of brown adipose tissue in cold stress?
It generates heat through non-shivering thermogenesis
How can cold acclimation affect brown adipose tissue activity?
It increases functional activity and reduces reliance on shivering
What are the primary consequences of reduced splanchnic blood flow during heat stress?
Local hypoxia, reduced renal and hepatic function, and increased microbial translocation
What is the functional importance of microbial translocation in heat stress?
It can lead to sepsis and multiple organ failure
What is the primary physiological response to skin temperature below 35°C?
Hypothermia and nervous system impairment
How does heat stress impact the cardiovascular system?
It increases heart rate and redistributes blood to the skin
What physiological response occurs when skin blood flow is high?
Increased heat dissipation and sweat evaporation efficiency
What happens during extreme heat stress if sweat evaporation is insufficient?
Core temperature rises continuously, risking heat-related illnesses
How do thermosensitive ion channels affect behavioural responses?
They drive behaviours like adjusting clothing and seeking cooler environments
What is the lowest recorded surviving core temperature?
13°C during extreme hypothermia
How does the body adapt to repeated heat stress?
Faster onset of sweating and vasodilation in acclimated individuals
What is the impact of heat stress on kidney function?
Reduced glomerular filtration rate and tubular reabsorption
What is the significance of convection in heat transfer?
It moves heat from the skin to the air via fluid movement
What is the physiological importance of increasing core temperature during exercise?
It helps balance heat gain and loss through effective responses
What is a common cause of heat-related deaths in elderly individuals?
Cardiovascular collapse due to vasodilation and insufficient cardiac output
What did studies on sugarcane workers reveal about heat stress?
It increases the risk of chronic and acute kidney injuries
How does sweating differ in humid environments?
Sweat evaporation is reduced, limiting cooling efficiency
What is the relationship between sweat evaporation and cooling?
1 gram of evaporated sweat removes approximately 2400 joules of heat
How does heat stress affect microbial integrity in the gut?
Decreased blood flow damages epithelial barriers, increasing translocation
What is the primary thermoregulatory function of brown adipose tissue?
Uncoupling protein 1 (UCP1) facilitates heat production without ATP synthesis
What physiological changes occur with cold acclimation?
Enhanced brown adipose tissue activity and reduced shivering reliance
How does heat stress influence renal blood flow?
It decreases renal perfusion, impairing filtration and reabsorption
What did Minson et al.’s study show about skin temperature changes?
Rapid increases in skin temperature drive heat dissipation responses
How does thermoregulation prioritize blood distribution?
It favors skin perfusion over splanchnic circulation to enhance cooling
What role does behavioural thermoregulation play in heat stress?
It minimizes energy costs by modifying the environment or activity
What is the role of heat shock proteins during hyperthermia?
They protect cells from thermal damage by stabilizing proteins
What is the physiological threshold for hypothermia?
Core temperatures below 35°C initiate hypothermia effects
What is the role of splanchnic vasoconstriction during heat stress?
It helps maintain blood pressure by reducing blood flow to central organs
