Page 195 - The Miracle of Hormones

A Wonderful Messenger:
Nitric Oxide

blood vessels dilate to respond to an in-
creased need for blood, and constrict after
we receive a wound to reduce bleeding.
How do the blood vessels know when
to dilate and when to constrict? The answer
to this question is very important for human
life. It is clear that a slight error that may hap-
pen at any point in the 100,000-kilometer
long network of blood vessels will inelucta-
bly have negative consequences.

The system of blood vessels in our bodies is
more complex than the highway network in a
developed country like Japan.