Exercise and Thermal Regulation Flashcards
What is our thermoneutral zone?
Where our body temperature is easily maintained and we are comfortable at which is in a 28-30º environment
What is the behaviour of our core body temp
Goes between 36.5 - 37.5 daily
Lowest at 4am, highest at 4pm
Stimulated by changes in light so will change when entrained
Ways to maintain heat balance and heat transfer
Conduction
Convection
Radiation
Evaporation and/or Metabolism
What is the effect of humidity on heat loss
If there is a high amount of water in the air it is harder for sweat to evaporate
Sweat the same regardless just changes in whether it can evaporate or not, will also feel hotter
How to we produce heat via metabolism
70% from basal metabolism - basic functions of internal organs keeping us alive (brain, liver, kidney, GIT)
How much of ATP usage during exercise is released as heat?
75%
How does brown adipose tissue keep babies warm?
High density of mitochondria which undergo oxidative phosphorylation and produce large amounts of heat
How do temp reflexes control core temp?
thermoreceptors ->
VOLUNTARY
central cortex -> skeletal muscle to shiver
INVOLUNTARY
hypothalamus -via sympathetic nerves> sweat glands, skin arterioles, adrenal medulla(->epinephrine)
Which part of the brain contains the thermoregulatory centre?
Hypothalamus
What happens with core body temp and heat production during exercise?
Both increase until they reach a tolerance limit
What is the tolerance limit?
Heat loss mechanisms cant keep up with heat production and core temperature climbs to dangerous levels
What is temperature acclimatisation?
Our tolerance limit can change and we can climatise to environments and exercise demands where our core temp can get up to 42º in elite athletes
- heat loss mechanisms kick in faster
- sweat composition has less salt to maintain homeostasis
- earlier onset of sweating
What is temperature acclimatisation and how does it aid heat loss?
Our tolerance limit can change and we can climatise to environments and exercise demands where our core temp can get up to 42º in elite athletes
- heat loss mechanisms kick in faster
- sweat composition has less salt to maintain homeostasis
- earlier onset of sweating
What happens in heat exhaustion? What effects does it cause in BP?
MABP = CO x TPR
Heat loss mechanisms include vasodilation which decreases TPR and sweating causes dehydration and a decrease in SV which both decrease BP
What happens in heat stroke and why is it so dangerous?
Heat loss mechanisms plateau and core temperature keeps increasing
heat gain > heat loss
Need to lose heat quickly or we will die
What happens to our thermoregulation when we get a fever?
The set point in the hypothalamus changes and is suddenly higher making us feel cold and heat loss mechanisms increase, get vasoconstriction and an increase in temperature
What happens to our thermoregulation when we get a fever?
The set point in the hypothalamus changes and is suddenly higher making us feel cold and heat loss mechanisms increase, get vasoconstriction and an increase in temperature
Get fever breaks where set point suddenly lowers and we get too hot
What happens when we get an fever from infection?
macrophages release release chemical messengers: endogenous pyrogens
Pyrogens are heat generating compounds (pyromaniac, fire, heat)
Interleukin 1 and 6
Why do surgeons let patients get hypothermic/drop body temp in surgery?
Decreases sympathetic nerve activity, less blood flow = less blood loss, metabolism drops by 8% per degree and therefore need less drugs administered, less O2 demand and therefore tissue can stay healthy for longer, reduction in release of pro inflammatory cytokines and therefore less inflammation
ATP is used to convert …… energy into ……..
ATP is used to convert chemical energy into mechanical movement
ATP is produced by 4 mechanisms which are:
Creatine Phosphate phosphorylation
Glycolysis
Oxidative Phosphorylation
Fatty Acid oxidation
What is the byproduct of glycolysis?
Lactic Acid
How many ATPs does a glucose make?
2
How many ATPs does Oxidative Phosphorylation make?
36 !
slow efficient aerobic
How many ATPs does a fatty acid make?
lots and lots more than any other mechanism
Do we still use ATP after exercising?
YES! We need to restore our energy supply.
Creatine back to creatine phosphate
Lactate back to glucose
How are our cardiovascular, respiratory and cellular (ATP synthesis) systems co-ordinating a response after exercise?
ATP requirements for restoration mean we are undergoing oxidative phosphorylation, which requires O2, therefore need an increase in blood flow and ventilation to remove metabolites and deliver O2 more than usual.
What are pyrogens?
Pyrogens are heat generating compounds (pyromaniac, fire, heat)
Interleukin 1 and 6
What is our anaerobic threshold?
Lactate threshold
When we go over 70% of our maximal intensity, oxidative phosphorylation isnt enough to generate ATP to sustain the intensity and glucose goes down the glycolytic pathway and makes lactate
Where is lactate made back into glucose?
In the liver
What occurs in oxygen debt?
Increased post -exercise oxygen consumption
Recovering energy stores
Processing lactic acid
Depends on rate of energy expenditure
When would we have a bigger O2 debt?
After higher intensity/strenuous exercise
ATP is required to clear lactic acid after exercise (T/F)
True
What prevents a drop in muscle fibre ATP conc during the first few seconds of intense exercise?
Creatine phosphate is converted into creatine and ATP
How much does arterial CO2 in/decrease during moderate and intense exercise?
Arterial CO2 remains constant in moderate exercise and falls with intense exercise as ventilation is higher than CO2 production
How much does venous CO2 in/decrease during exercise?
Venous CO2 increases with increased CO2 production
How much does arterial and venous O2 in/decrease during moderate and intense exercise?
Arterial O2 remains constant
Venous O2 decreases with increased consumption
Ventilation during exercise is controlled by:
keeping arterial gases the same to maintain pH
What is the central command for thermoregulation in exercise?
Exercise increases cardiovascular and respiratory circuits in the CNS
Proportional to the amount of skeletal muscle contraction
An increase in core temperature stimulates an increase in what?
ventilation - to lose heat from panting
How does exercise signal an increase in respiration?
Muscle mechanoreceptors detect contractions
Lactic acid increases arterial [H+] and muscle damage = release of K+ from muscles which are both detected by peripheral chemoreceptors
Adrenaline from adrenal glands stimulates cardio and respiration
How does lactic acid effect respiration?
The generation of lactic acid increases arterial [H+]
We need to increase O2 consumption to buffer out the acid. Metabolic acidosis activates peripheral chemoreceptors which are responsive to an increased H+ concentration.
How does sympathetic activity effect regional blood flow?
Noradrenaline is released from sympathetic nerves and cause a global systemic vasoconstriction
If there is a global systemic vasoconstriction of vessels during exercise, how does blood flow to skeletal muscle increase?
Local metabolites and mechanical compression override the constriction and cause dilation
How does muscle contractions change blood flow?
Compression of blood vessels cause baroreceptors to cause dilation as a reflex to control blood pressure
What occurs in the baroreceptor reflex?
Baroreceptors detect a stretch from an increase in MABP, they increase frequency of communication to the barosensitive cells in the NTS, which then excite the barosensitive cells in the CVLM, inhibiting the RVLM, decreasing sympathetic stimulation and decreasing MABP
How can we modify the baroreceptor reflex?
Central command DIRECTLY stimulates the RVLM to continue sympathetic stimulation, and INDIRECTLY activates inhibitory cells in NTS, inhibiting barosensitive cells so the baroreceptor signals aren’t responded to
Why would we override the baroreceptor reflex?
We need to not decrease our BP when we are exercising to keep high blood flow to skeletal and cardiac muscle
We don’t want the baroreceptor reflex so have modified the reflex to keep up the BP
Local release of metabolites in exercising skeletal muscle overrides the global vasoconstriction induced by noradrenaline (T/F)
True
Assertion:
The bear-reflex is modified in exercise permitting an increase in MABP
BECAUSE
central command decreases the sensitivity of baroreceptors
TRUE/FALSE
Central command decreases the sensitivity of barosensitive cells in the NTS by activating inhibitory cells
What is the initial energy source at onset of exercise?
Creatine Phosphate
What is the order of activation of fuel sources?
Creatine Phosphate
Anaerobic glycolysis
Anaerobic oxidation
Aerobic oxidation
What is the main fuel source after half an hour?
Aerobic oxidation
- Plasma FFA and adipose tissue triglycerides
What is myofibrillar hypertrophy?
Due to increase in anaerobic training, muscle fibres increase in size NOT number due to increase acting and myosin - adding more contractile units within the fibre and increasing muscle size and strength.
What is the micro-trauma theory?
Maximal loads cause micro tears within the muscle fibres, leading to activation of satellite repair cells to bridge the damage
What is sarcoplasmic hypertrophy?
Sarcoplasmic hypertrophy occurs when we get an increased volume in sarcoplasm
