Redistribution of Blood During
Exercise
Shunting or Accommodation
Blood
flow
changes
during
exercise
Shunting or Accommodation
• Blood flow changes dramatically once
exercise commences.
• At rest, only 15-20% of cardiac output is
directed to skeletal muscle (the majority of
it goes to the liver (27%) and the kidneys
(22%).
• Blood is redirected to areas where it is
needed most.
• This is known as Shunting or
Accommodation.
Blood
flow
changes
during
exercise
Redistribution of Blood
• The redistribution of blood is controlled primarily
by the vasoconstriction and vasodilation of
arterioles.
• It reacts to chemical changes of the local
tissues. For example, vasodilation will occur
when arterioles sense a decrease in oxygen
concentration or an increase in acidity due to
higher CO2 and lactic acid concentrations.
• Sympathetic nerves also play a major role in
redistributing blood from one area of the body to
another.
Redistribution of Blood
• The smooth muscle layer (tunica media) of
the blood vessels is controlled by the
sympathetic nervous system, and remains
in a state of slight contraction known as
vasomotor tone. By increasing
sympathetic stimulation, vasoconstriction
occurs and blood flow is restricted and
redistributed to areas of greater need.
• When stimulation by sympathetic nerves
decreases, vasodilation is allowed which
will increase blood flow to that body part.
Redistribution of Blood
• Further structures which aid blood
redistribution are pre-capillary sphincters.
Pre- capillary sphincters are ring shaped
muscles which lie at the opening of
capillaries and control blood flow into the
capillary bed.
• When the sphincter contracts, it restricts
blood flow through the capillary, and
deprives tissues of oxygen; conversely
when it relaxes, it increases blood flow to
the capillary bed.