Mechanisms of Blood Flow Control
Local blood flow control can be divided into two phases: (1) acute
control and (2) long-term control.
Acute control is achieved by rapid changes
in localvasodilation or vasoconstriction of the arterioles, metarterioles, and
precapillary sphincters, occurring within seconds to minutes to provide very
rapid main-tenance of appropriate local tissue blood flow.
Long-term control, however, means slow,
controlledchanges in flow over a period of days, weeks, or even months. In
general, these long-term changes provide even better control of the flow in
proportion to the needs of the tissues. These changes come about as a result of
an increase or decrease in the physical sizes and numbers of actual blood
vessels supplying the tissues.