special situation- exercise

Question 1

how can the response to exercise be viewed ?

Answer 1

• 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)

Question 2

what are the 2 types of exercise ?

Answer 2

• 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

Question 3

what are the local effects in exercising muscle?

Answer 3

• 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

Question 4

what else also causes vasodilation in vessels ?

Answer 4

• 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

Question 5

what is VD counteracted by ?

Answer 5

• the mechanical influences of muscle contraction during exercise
• during rhythmic exercise this is intermittent

Question 6

what happens to local blood flow to muscles during exercise?

Answer 6

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

Question 7

which receptors are involved during the exercise reflex ?

Answer 7

• muscle sensory afferents
• metaboreceptors
• joint receptors too (little)-> mechanoreceptors

Question 8

where do these sensory afferents converge ?

Answer 8

• at the sub thalamic locomotor region

- exercise integrating area

Question 9

what are the responses of the exercise reflex ?

Answer 9

• 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

Question 10

how is blood diverted away from the gut during exercise ?

Answer 10

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

Question 11

how is VC in skeletal muscle overcome during exercise ?

Answer 11

• process known as exercise hyperaemia –> functional sympatholysis
• allows for increase muscle blood flow

Question 12

what is the evidence for the role of central command (SLR) in exercise?

Answer 12

• 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

Question 13

why is pressure auto-regulation important ?

Answer 13

• 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

Question 14

why is the thermoregulatory reflex important ?

Answer 14

• 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

Question 15

what does the BRR do?

Answer 15

• it helps buffer the rise in ABP

- but allows the set point to be increased too

Question 16

do chemoreceptors have a role in exercise ?

Answer 16

• 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

Question 17

when do peripheral chemoreceptors contribute ?

Answer 17

• 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

Question 18

how do the responses in static exercise differ to dynamic ?

Answer 18

• 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

Question 19

how does exercise hyperaemia differ ?

Answer 19

• 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

Question 20

why may ABP Fall after state exercise ?

Answer 20

• reactive exercise hyperaemia occurs after static exercise
• a large quick drop in ABP
• may cause fainting after lifting heavy weights

Question 21

what does mental stress active ?

Answer 21

• the altering or defence response
• can precede exercise
• or occur independently of it

Question 22

what occurs during the defence response ?

Answer 22

• Increased CO, increased ABP, VC In viscera/skin

- Skeletal Muscle vessels -> Vasodilatation

Question 23

how can we examine the alter t response ?

Answer 23

• Altering response –> use of stroop test as an alternative stressor experimentally
  
  • Flashing these colours gets people stressed

Question 24

how do we get vasodilatation in the skeletal muscle during the mental response ?

Answer 24

• reduced SNS NA activity to muscle both via RVLM
• increased circulating ad which acts on B2 - AR (from adrenal medulla)
• RVLM

Question 25

what are the characteristics of response to mental stress?

Answer 25

• 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)

Question 26

why can ABP reach very high levels during the response to mental stress ?

Answer 26

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

Question 27

when is a rise in ABP a risk?

Answer 27

• those with COD, MI, aneurism , fragile cerebral BVs (acute)
• repeated emotional stress who do not habituate early can lead to essential hypertension (chronic)

Question 28

what leads to essential hypertension development ?

Answer 28

• 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