Vasoconstriction is the process where blood vessels narrow, reducing blood flow. This occurs when the smooth muscles in the vessel walls contract, often in response to cold temperatures or stress. It helps regulate blood pressure and directs blood to vital organs during emergencies. This physiological response is controlled by the nervous system and can be influenced by hormones like norepinephrine. Vasoconstriction plays a crucial role in maintaining body temperature and ensuring that essential organs receive adequate blood supply when needed.