CV regulation during exercise Flashcards
What are the neural factors that contribute to CV adjustments during exercise?
central command
reflexes originating in the contracting muscle
baroreceptor reflex
What is the central command?
the cerebrocortical activation of the sympathetic nervous system that produces cardiac acceleration, increases myocardial contractile force, and peripheral vasoconstriction
How can reflexes be activated?
intramuscularly by stimulation of mechanoreceptors (stretch, tension) or chemoreceptors in response to contraction (metaboreflex)
Where do impulses from mechano or metaboreceptors travel?
centrally via small myelinated (group III) and unmyelinated (group IV) afferent nerve fibres
What do group IV unmyelinated fibres represent?
muscle chemoreceptors
What is the efferent limb of the metaborelfex composed of?
the sympathetic nerve fibres to the heart and peripheral blood vessels
What does anticipation of PA cause?
inhibition of the vagus nerve impulses to the heart
*underlies the initial increase in HR
What is the response from mild to moderate exercise?
inhibition of parasympathetic areas and activation of sympathetic areas of the medulla increase the HR and myocardial contractility
increases CO = raise in arterial pressue
What vascular change does the sympathetic nervous system elicit during exercise?
resistance changes in peripheries
vasoconstriction increases vascular resistance, diverting blood away from the skin, kidneys, splanchnic regions, and inactive muscle
*persists through exercise
What can the increase in blood flow to active muscle be attributed to?
the modest elevation of blood pressure or an unknown mechanism
Why can’t the increase in blood flow to active muscle be attributed to a neural mechanism?
a chemical block of the autonomic NS does not alter this blood flow response
What occurs as CO and blood flow to active muscles increases with intensity?
visceral (splanchnic and renal) blood flow decreases
blood flow to the heart increases, unchanged to the brain
What is the response in skin blood flow during exercise?
initially decreases
then increases as body temp rises with increments in duration and intensity
finally decreases when skin vessels constrict as total body VO2 nears max
What causes dilation during exercise?
local formation of vasoactive metabolites
progresses as intensity increases
What is K+ role in exercise?
released by contracting muscle and may be responsible for the internal decrease in vascular resistance in active muscle
*elevated interstitial K+ can cause vasodilation by stimulating the Na-K pump and activation of other channels
How does K+ affect Ca+2 entry?
causes hyperpolarization of vascular smooth muscle membrane reducing Ca2+ entry
What are the factors for locally dilating arterioles during exercise?
adenosine
NO
KATP channels
decreased pH
What does the local accumulation of metabolites cause?
relaxes terminal arterioles
blood flow may rise 15 to 20 times about resting in the muscle
*occurs very soon after the onset of exercise
What does the decrease in TPR enable?
the heart to pump more blood at a lesser load and more efficiently (less pressure work)
What is capillary recruitment during exercise?
at rest, only a small amount of capillaries are perfused
in actively contracting muscle, nearly all capillaries contain flowing blood
What happens to AVO2 diff during exercise?
increases
*oxyhemoglobin dissociation
What factors contribute to a right shift of the oxyhemoglobin dissociation curve (less offloading/increased affinity)?
decreased pH (CO2 and lactic acid formation)
increase in temperature
*Bohr effect
At any given partial pressure of O2, what is the effect of O2 Hb binding?
less O2 is bound to Hb in RBC
O2 removal from blood in facilitated
What is the relationship between O2 consumption and muscle blood flow?
O2 consumption may increase 60-fold with only a 15-fold increase in muscle blood flow
*not 1:1
What is the role of muscle myoglobin during exercise?
serves as a limited O2 store in exercise
can release attached O2 at very low partial pressures
*facilitates O2 transport from capillaries to mitochondria by serving as an O2 carrier
