ABSTRACT
Because not every cell in the human body is near enough to the environment to easily exchange with it mass (including nutrients, oxygen, carbon dioxide, and the waste products of metabolism), energy (including heat), and momentum, the physiologic system is endowed with a major highway network-organized to make available thousands of miles of access tubing for the transport to and from a different neighborhood (on the order of 10
µ
m or less) of any given cell whatever it needs to sustain life. This highway network, called the
cardiovascular system,
includes a pumping station, the heart; a working fluid, blood; a complex branching configuration of distributing and collecting pipes and channels, blood vessels; and a sophisticated means for both intrinsic (inherent) and extrinsic (autonomic and endocrine) control.
