Myogenic Mechanisms Regulating Blood Flow
Myogenic mechanisms are intrinsic to vascular smooth muscle, particularly in small arteries and arterioles. If the pressure within a vessel is suddenly increased, the vessel responds to the sudden stretching of the wall by constricting. Diminishing pressure within the vessel causes relaxation and vasodilation. The response to vascular stretch is observed in vivo and in isolated, pressurized blood vessels.
The myogenic mechanism may play a role in autoregulation of blood flow and in reactive hyperemia. Either partial or complete occlusion of a supply artery causes the pressure downstream to fall, which elicits myogenic relaxation of vascular smooth muscle in the downstream resistance vessels. Myogenic behavior has not been identified in all vascular beds, but it is prominent in the cerebral, splanchnic and renal circulations, and may be present to a small degree in skeletal muscle.
Electrophysiological studies have shown that vascular smooth muscle cells depolarize when stretched, leading to contraction. Stretching also increases the rate of smooth muscle pacemaker cells that spontaneously undergo depolarization and repolarization.