Vasoconstriction

vasoconstriction

Vasoconstriction is the narrowing of blood vessels that happens when the smooth muscle in their walls tightens. This tightening reduces the space through which blood can flow, so less blood gets past that point. It is a normal body response used to control blood pressure and to conserve heat when the environment is cold. The nervous system and several chemical messengers tell vessels when to tighten and when to relax. Substances such as adrenaline, angiotensin, and endothelin commonly trigger this response, while other signals cause relaxation. In short bursts it is helpful — for example, it redirects blood to vital organs during stress or injury. But if vessels stay narrowed too long, or if they tighten in the wrong place, tissues can be starved of oxygen and nutrients. That can lead to problems like high blood pressure, pain from poor circulation, organ damage, or worsening of chronic diseases.