Download cardiovascular adjustments to exercise

BY : DR FARIHA RIZWAN
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The cardiovascular adjustments at the beginning of
exercise are rapid .
Within one second after the commencement of
muscular contraction there is an increase in sympathetic
stimulation of the heart
At the same time, there is a vasodilation of arterioles in
active skeletal muscles and a reflex increase in the
resistance of vessels in less-active areas.
The end result is an increase in cardiac output to
ensure that blood flow to muscle matches the
metabolic needs .
What is the signal to "turn on" the cardiovascular system
at the onset of exercise?
Answer to this question have led us to the development
of the central command theory
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The term central command refers to a motor signal
developed within the brain.
The central command theory of cardiovascular control
argues that the initial cardiovascular changes at the
beginning of dynamic exercise (e.g., cycle ergometer
exercise) are due to centrally generated cardiovascular
motor signals, which set the general pattern of the
cardiovascular response.
However, it is believed that cardiovascular activity is
modified by heart mechanoreceptors, muscle
chemoreceptors , muscle mechanoreceptors, and
pressure-sensitive receptors (baroreceptors) located
within the carotid arteries and the aortic arch
Muscle chemoreceptors are sensitive to increases in
muscle metabolites (e.g., potassium, lactic acid, etc)
They send messages to higher brain centers to "fine
tune" the cardiovascular responses to exercise
Muscle mechanoreceptors (e.g., muscle
spindles, golgi tendon organs) are sensitive to
the force and speed of muscular movement
 These receptors, like muscle chemoreceptors,
send information to higher brain centers.
 Baroreceptors, which are sensitive to changes
in arterial blood pressure,send afferent
information back to the cardiovascular control
center to add precision to the cardiovascular
activity during exercise.
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 The
central command theory proposes
that initial signal to the cardiovascular
system at the beginning of exercise
comes from Higher brain centers.
 fine-tuning of the cardiovascular response
is accomplished via a series Feedback loops
muscle chemoreceptors , muscle
mechanoreceptors and arterial
baroreceptors