Biology 105
Biology of Exercise
Spring 2003
4/11/03 - Post-class outline
Learning objectives:
How to interpret statistical information.
How does the circulation carry blood to the tissues?
Diagrams
Changing the distribution of blood flow can increase blood flow to exercising
muscle.
- flow = pressure gradient / resistance
- the pressure gradient is determined by the difference in arterial and
venous pressures, this is mainly a function of the activity of the heart,
and will not vary very much from one tissue to another.
- the resistance is determined primarily by the radius of the arteries
just before the capillary beds.
- resistance = (viscosity of blood * length of vessel) / radius 4
- vessel radius can be controlled by the nervous system.
- contraction of vessels (vasoconstriction) leads to increased resistance
and thus to lower flow through a tissue
- relaxation of vessels (vasodilation) leads to decreased resistance
and thus to higher blood flow.
- During exercise, blood pressure could fall if no adjustments were made.
- Why?
- Increased flow to muscles and skin will leave less flow returning to
the heart.
- This decreases venous pressure, decreases filling pressure.
- Thus, SV is decreased and CO falls.
- When CO falls, arterial pressure falls as well.
- blood flow = pressure gradient / resistance
- pressure gradient = resistance * flow (CO)
- The baroreflexes help control blood pressure.
- During exercise, blood pressure often is elevated above normal
- The volume problem during exercise.
- Not only is increased flow to skin and muscles required during exercise,
but often blood volume becomes reduced as well.
- Why?
- Sweating causes reduction in blood volume due to loss of water.
- Increased blood pressure causes increased fluid filtration out of the
capillaries.
