Vasoconstriction

Vasoconstriction is the physiological process in which blood vessels narrow due to the contraction of smooth muscle cells in their walls. This narrowing reduces the diameter (lumen) of the vessel, leading to decreased blood flow and increased vascular resistance. It is a critical mechanism for regulating blood pressure, redistributing blood flow, conserving body heat, and responding to various stimuli such as cold temperatures or stress.

Other names

Vascular constrictionBlood vessel narrowing

Contraction of vascular smooth muscle cells triggered by an increase in intracellular calcium concentration. Calcium enters via voltage-gated channels or is released from intracellular stores (sarcoplasmic reticulum) through IP3-mediated pathways. Calcium binds calmodulin, activating myosin light-chain kinase (MLCK), which phosphorylates myosin light chains and initiates cross-bridge cycling with actin filaments—resulting in contraction.