special situation- exercise Flashcards
how can the response to exercise be viewed ?
- Local VD in exercising muscle ->which is superimposed
- Exercise reflex–>CVS as a whole-> co-ordinated by CNS
Cortical influences (volition)–> higher brain influencing reflex function-> depends on type of exercise, motivation to take part in exercise (central command)
- Exercise reflex–>CVS as a whole-> co-ordinated by CNS
what are the 2 types of exercise ?
- Dynamic (rhythmic)- running, jogging and cycling (moving joints)
- Static (isometric)- sustained contraction-> hand grip, holding heavy weight, pushing against immovable object
- Both have different effects on CVS
what are the local effects in exercising muscle?
- exercise hyperaemia -> local VD of skeletal muscle vessels
- K efflux (down stroke) , Pi, adenosine released by contracting muscle into interstitial space
- K acts on smooth muscle dilating it via hyperpolarisation
- Pi acts on adenosine receptors also causing relaxation of V smooth muscle by increasing cAMP
what else also causes vasodilation in vessels ?
- during dilation there is increased blood flow acting on endothelium (increased shear stress) causing it to release potent VD such as PGi2 and NO which act on the muscle fibres
- cocktail causes relaxation of V smooth muscle -> VD
what is VD counteracted by ?
- the mechanical influences of muscle contraction during exercise
- during rhythmic exercise this is intermittent
what happens to local blood flow to muscles during exercise?
Muscle blood flow actually fluctuates increasing and decreasing continuously–> BV running through muscle squeezed during muscular fibre contractions closing the vessel lumen
- Functional hyperaemia occurs during the relaxation phases between the contractions - During contractions blood flow decreases - Blood flow does go up--> mean change during exercise Is being mechanically occluded--> greater with stronger contractions
which receptors are involved during the exercise reflex ?
- muscle sensory afferents
- metaboreceptors
- joint receptors too (little)-> mechanoreceptors
where do these sensory afferents converge ?
- at the sub thalamic locomotor region
- exercise integrating area
what are the responses of the exercise reflex ?
- Increased respiration (increased motor activity to diaphragm + intercostals)
- Increased HR and contractility (increased SNS, reduced PNS vagal due to coupling of inspiration and vagal nerve fibres, RSA)
- Increased CO and increased SP
how is blood diverted away from the gut during exercise ?
SLR–> medulla–> influences and increases outflow to SNS fibres
- Increased noradrenergic activity to cause reflex VC to G.I.T, kidney, skin, and all skeletal muscle - Increased TPR and increases DP
how is VC in skeletal muscle overcome during exercise ?
- process known as exercise hyperaemia –> functional sympatholysis
- allows for increase muscle blood flow
what is the evidence for the role of central command (SLR) in exercise?
- changes in ABP occur when person attempts to contract under paralysis
- responses evoked by direct stimulation of muscles to male them contract are smaller than during volitional contraction
- brain imaging shows cortical areas are active during volitional exercise
why is pressure auto-regulation important ?
- occurs in cerebral circulation
- if ABP rises there is myogenic constriction keeping flow constant to the brain
- protects cerebral vessels from damage during rise I BP
why is the thermoregulatory reflex important ?
- increase in body temp during exercise
- VC In the skin vessels is overcome by this reflex
- reduced SNS activity leading to cutaneous VD
- reducing DP and mean ABP
what does the BRR do?
- it helps buffer the rise in ABP
- but allows the set point to be increased too
do chemoreceptors have a role in exercise ?
- no obvious role of both central (CO2) or peripheral (02) as arterial gases remain constant as long and VE matches Pco2 (due to exercise reflex) –> via metaboreceptors here
- however some circulation K from muscle contraction can stimulate the peripheral CR increasing their excitability and firing
- may increase VE but not via their normal stimuli of blood gases
when do peripheral chemoreceptors contribute ?
- during the reflex increase in VE once the anaerobic threshold is surpassed (exercise continues) –>lactate levels rise and are sensed by these PCR
- H+ ions stimulate them
- explains the shear increase in VE past this point increasing pa02 but reducing paco2
how do the responses in static exercise differ to dynamic ?
- Different on affect on BP
- SP and DP go up in proportion to level of contraction
- Graded increases in both SP and DP
- Reflex increases in–> respiration, HR
- Same mechanisms involved but…
Exercise hyperaemia occurs after contraction
how does exercise hyperaemia differ ?
- occurs after muscle contraction
In exercising muscle, exercise hyperaemia is overcome by effects of mechanical compression (occlusion) caused by muscle contraction
- Metabolites are trapped in contracting muscle - Causes greater stimulation of metaboreceptors
So the exercise reflex is greater for given work load than during dynamic exercise
why may ABP Fall after state exercise ?
- reactive exercise hyperaemia occurs after static exercise
- a large quick drop in ABP
- may cause fainting after lifting heavy weights
what does mental stress active ?
- the altering or defence response
- can precede exercise
- or occur independently of it
what occurs during the defence response ?
- Increased CO, increased ABP, VC In viscera/skin
- Skeletal Muscle vessels -> Vasodilatation
how can we examine the alter t response ?
- Altering response –> use of stroop test as an alternative stressor experimentally
- Flashing these colours gets people stressed
how do we get vasodilatation in the skeletal muscle during the mental response ?
- reduced SNS NA activity to muscle both via RVLM
- increased circulating ad which acts on B2 - AR (from adrenal medulla)
- RVLM
what are the characteristics of response to mental stress?
- Isnt stereotyped like BRR or exercise reflexes are–> show habituation or sensitization
- If stimulus increases response can either increase (hypersensitization) or decrease (habituation)
- Common to all mammalian species
- Appropriate stimulus varies amongst individuals
- Response can be conditioned (response to crowd at sports arena)
why can ABP reach very high levels during the response to mental stress ?
descending tracts from defence cortical areas of brain can inhibit the BRR response
- Cant regulate BP effectively when stressed - Therefore ABP can reach very high levels when frightened or stressed
- therefore stress is the root cause of a lot of CVS diseases
when is a rise in ABP a risk?
- those with COD, MI, aneurism , fragile cerebral BVs (acute)
- repeated emotional stress who do not habituate early can lead to essential hypertension (chronic)
what leads to essential hypertension development ?
- environmental stressors via defence areas + genetic influences too
- chronic increase in ABP leads to hypertrophy of V smooth muscle
- BV grow inwards narrowing lumens
- reason why TPR and ABP rise
- is a loop
