Autoregulation

Flow in blood vessels and vascular beds can remain constant despite large changes in perfusion pressure within a certain range. This is achieved by autoregulation - a mechanism that alters the diameter of blood vessels and, therefore, resistance, according to the change in perfusion pressure. Autoregulatory processes involve intrinsic mechanisms that are independent from extrinsic neurohumoral influences, and contribute to basal tone, on top of which other influences are imposed. Possible mechanisms of myogenic and metabolic autoregulation (the main autoregulatory processes in most vascular beds) are examined in this review. Tubuloglomerular feedback (an autoregulatory process that is exclusive to the kidney) is also discussed. Several other mechanisms can act locally within blood vessels, causing vasodilation, vasoconstriction or both. They contribute to basal vascular tone and so indirectly affect autoregulation, and are also examined (along with extrinsic controls); the contribution of autoregulation to vascular tone in individual vascular beds is discussed in this context.