Biology 105
Biology of Exercise
Spring 2003
4/9/03 - Post-class outline
Learning objectives:
How to interpret statistical information.
How does the circulation carry blood to the tissues?
Diagrams
The circulatory system
During exercise, demand for flow will increase dramatically in certain tissues.
- muscles need increased flow to sustain contractions
- skin may need increased flow to dissipate heat
- heart and brain will at least need flow maintained.
- table of blood flow during exercise and rest.
There are two ways to accommodate this need for increased flow increase total
flow through the system (cardiac output): increase stroke volume or increase
heart rate.
- Cardiac output (CO) = stroke volume (SV) * heart rate (HR).
- Stroke volume is the amount of blood pumped by each heart beat.
- SV depends both on
- amount of filling of heart between contractions (the period between
contractions is called diastole). This is called the end
diastolic volume (EDV)
- the strength of the heart contraction (the time when the heart is contracting
is called systole). the strength of contraction will determine
the amount of blood left in the heart after contraction, this is the end
systolic volume (ESV).
- SV = EDV - ESV.
Changing the distribution of blood flow also 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
How is the circulatory system regulated?
- Output from the brain falls into two major categories, somatic (voluntary)
and autonomic (involuntary)
- The somatic system is the portion of the PNS that carries information
to the skeletal muscles. It is responsible for the activation of muscles
during voluntary movement.
- The autonomic system is involved mainly with regulation of homeostasis,
most of these functions are not under voluntary control (such as regulation
of heart rate). The autonomic system has two opposing pathways, the sympathetic
system and the parasympathetic system.
- The sympathetic nervous system activates the systems of the body
that are required for strenuous physical activity. It is activated
in when danger or stress is perceived. It is often said to mediate
the "flight or fight" response.
- The parasympathetic system essentially opposes the sympathetic system.
It is activated after meals and during periods of relaxation. It is
often said to mediate the "rest and digest" response.
- Table of the effects of the sympathetic
system and the parasympathetic system.
