L27 - Thermoregulation 2 Flashcards
What must happen when body temperature decreases?
body heat must be conserved and additional heat (energy) must be produced
What will happen to heart rate at low temperatures?
depends on the exact temperature and individual
Why will decreased temperature result in decreased heart rate?
arterioles in the skin will constrict to conserve heat
this will increase TPR and as a result CO will decrease
How does the body conserve heat?
sympathetic noradrenergic neurons cause cutaneous vasoconstriction (non-apical skin)
piloerection to increase insulating layer (largely ineffective in clothed individuals)
What would happen to ventilation (at rest) at low temperature?
increase
this is because heat is produced through metabolism so in order to produce more heat metabolism ↑ and therefore ventilation ↑
What are the different ways in which the body produces heat?
- normal metabolism
- skeletal muscles: shivering thermogenesis, voluntary movements (EAT and NEAT)
- brown and beige adipose tissue (BAT): non-shivering thermogenesis
What is EAT and NEAT?
exercise-associated thermogenesis and non-exercise activity thermogenesis
Why does ventilation increase when there is overall increased metabolic activity?
increased O2 demand / CO2 production
What are characteristics of shivering thermogenesis?
indicates maximum vasoconstriction, initiated by peripheral thermoreceptors (skin), activated by hypothalamus and motor cortex
Where does non-shivering thermogenesis occur?
occurs in brown and beige adipose tissue (BAT)
What does brown and beige adipose tissue contain?
high levels of uncoupling protein-1 which derails the electrochemical gradient for ATP synthesis in mitochondria, and causes the release of energy
What is non-shivering thermogenesis regulated by?
thyroid hormone and sympathetic nervous system
What are behavioural adaptations to cold?
warm clothing, “huddle up” to minimise exposed surface, seek shelter, stay well nourished
What is fever?
↑ in set-point temperature induced by pyrogens
generally in response to pathology such as infection
aids to mobilise immune system
What are exogenous and endogenous pyrogens?
endotoxins from bacteria are exogenous and cytokines are endogenous
How do pyrogens result in fever?
pyrogens influence the hypothalamus resulting in an elevated thermoregulatory set point and fever
What is the purpose of fever?
↑ T-cell generation and differentiation (enhances immune response)
may inhibit the function and spread of bacteria/viruses directly
Is fever the enemy?
no, it is a response induced by the body to aid in the immune response
not harmful unless over 42˚C
What is shivering a sign of?
the onset of fever
What are chills (caused by fever)?
heating mechanisms activated as set-point rises (shivering)
What happens when fever ends?
cooling mechanisms activated as set-point falls (sweating)
What is there a conflict between during exercise in the heat?
skin blood flow, skeletal muscle blood flow and
fluid loss
When exercising in the heat, fluid loss will result from:
sweating - 2-3 L/hour in trained individuals (~1 L/hour in untrained)
increased ventilation
After significant fluid loss during exercise which parameters will decrease (compared to exercise at the same intensity before fluid loss)?
venous return, stroke volume, MAP, blood flow to inactive skeletal muscle and blood flow to skin
If a person loses 6 litres of water through sweat and ventilation without consuming more water, how much will their plasma volume drop?
1/3 of body’s water is in the ECF and 1/4 of the ECF volume is plasma
therefore 6 x 1/3 x 1/4 = 0.5 L or 500 mL
If a person loses 6L of water through sweat and ventilation during exercise, we would expect to see an increase in:
sympathetic nervous system activity, ANGII, aldosterone, vasopressin, sodium reabsorption, water reabsorption
How is MAP restored?
increased SNS and decreased PNS activity resulting in increased CO (HR) and increased TPR
How is plasma volume restored?
recruitment of the renin-angiotensin system which will lead to production of ANG II (↑ PCT reabsorption) and aldosterone (↑ Na+ reabsorption in the collecting duct)
What stimulates activation of RAS?
the SNS
What does it means if RAS is activated?
ANP is decreased resulting in increased Na+ reabsorption in the collecting duct
What happens when water volume is low?
results in increased osmolarity and vasopressin release which is going to increase H2O reabsorption in the collecting duct
What happens when water volume is particularly low?
ANGII will increase vasopressin release
