The
Microcirculation
193
contributors to peripheral vascular resistance that can effectively alter
cardiac output.
Fig.7.1.1:
A
network
of
microcirculatory unit, illustrating the constituent components.
The structural components of the microcirculation are classified into
resistance, exchange, shunt, and capacitance vessels.
The resistance
vessels,
comprising the
arterioles, metarterioles, and
precapillary
sphincters, serve primarily to decrease the arterial pressure to the levels
of the capillaries
to
facilitate effective exchange.
Differences in microvascular
behavior are
attributed
to
the
differences in the overall function of the body organ in which these
microvessels exist. Thus, flow in the microvessels of the brain differs
from that in the heart or the lungs. Some capillaries are fed by the
arterioles and collected by the venules, but others can bypass the
capillaries and connected directly to either small artery to a small vein.
These latter are known as anastomoses which serve to control flow and
certain transport processes.
As
well known in the countercurrent
mechanism for the body temperature control, the small arteries and veins
run parallel and frequently adjacent to each other, while branching
