The Blood Vasculature as an Adaptive System: Role of Mechanical Sensing

Abstract

The vascular system consists of an extensive network of conduits that carry blood to all parts of the body. The metabolic requirements of tissues, including oxygen demand, vary spatially and temporally. In order to meet these varying requirements, the vascular system must have the ability to adjust and control blood flow in space and time. Centrally driven neural and hormonal signals modulate flow at the whole-organ or regional level. Local modulation of blood flow is achieved by responses of individual microvessels to stimuli that they experience. The responses include acute changes of diameter achieved by alterations in the contractile state of smooth muscle in vessel walls (flow regulation), and long-term changes of vascular dimensions achieved by structural alterations in the vessel walls and by addition or loss of vascular segments (structural adaptation). Here, current understanding of these processes is reviewed, with emphasis on the role of vascular responses to mechanical stresses, i.e., wall shear stress resulting from blood flow and circumferential wall stress resulting from intravascular pressure, and the importance of these responses in flow regulation and structural adaptation. It is concluded that the blood vasculature is a sensitive adaptive system, in which mechanical sensing plays an important role in coordinating vascular responses.