Fractals in Physiology
|Some of the most visually striking examples of fractal forms are
found in physiology:
The respiratory, circulatory, and nervous systems are remarkable instances of fractal
architecture, branches subdividing and subdividing and subdividing again.
are provided in Goldberger, Rigney and West.
no clear genetic, enzymic, or biophysical mechanism yet have been shown to be responsible
for this fractal structure, few doubt this.
|Careful analysis of the lungs reveal fractal
scaling, and it has been noted that this fractal structure makes the lungs
more fault-tolerant during growth.
|Here are three pictures of lung casts, some with the
circulatory system casts included. These pictures were provided by Dr. Ewald R. Weibel.
The heart is filled with fractal networks: the coronary arteries and veins, the fibers
binding the valves to the heart wall, the cardiac muscles themselves, and the His-Purkinje
|In addition to falut-tolerance during growth, fractal branching
makes available much
more surface area for absorption and transfer in bronchial tubes, capallaries, intestinal
lining, and bile ducts.
|Kalda has proposed a fractal
model of the blood vessel system that achieves a homogeneous oxygen supply throughout the body.
|Also, the redundancy of fractal structures make them robust against
injury. For example, the heart can continue to function even after the His-Purkinje system
has suffered considerable damage.
|From his work on the ability of
fractal drums to damp
vibrations, Bernard Sapoval deduced another advantage of the fractal
character of the circulatory system: "the fractal structure of the human circulatory
system damps out the hammer blows that our heart generates." "The heart is a
very violent pump, and if there were any resonance in blood circulation,
you would die."
|Fractals may save our lives every minute.
Here are some casts of animal lungs.
|Finally, we note the body exhibits dynamical fractals.
| For example, it is well-known that
healthy heartbeats are chaotic rather than regular.
|A careful plot of heart rates over
several time scales reveals self-similar scaling
(Goldberger, Rigney and West).