Vasoconstriction

Vasoconstriction is the narrowing of blood vessels when their smooth muscle contracts. It increases vascular resistance and can reduce blood flow through affected vessels.

Vascular smooth muscle: Muscle cells in vessel walls that contract or relax to regulate vessel diameter. Its contraction directly narrows the vessel during vasoconstriction.
Vasodilation: Widening of blood vessels caused by relaxation of vascular smooth muscle. It is the direct diameter-changing counterpart to vasoconstriction.
Thermoregulation: The processes by which an organism maintains its internal temperature within a viable range. Skin-vessel constriction reduces heat transfer from the body to the environment.
Nitric oxide: A short-lived signaling molecule made by endothelial cells that relaxes vascular smooth muscle. It opposes constriction by promoting vessel relaxation.
Vascular tone: The degree of baseline contraction in blood-vessel smooth muscle. Vasoconstriction raises the vessel’s tone above its prior level.
Arteriole: A small artery that carries blood into capillary beds and helps regulate their perfusion. Arterioles are major sites where changes in diameter regulate resistance.
Sympathetic nervous system: The division of the autonomic nervous system that mobilizes the body during stress and activity. Its signaling can constrict vessels and redirect blood flow.
Endothelin: A family of peptides that can strongly constrict blood vessels through receptors on vascular smooth muscle. It is a potent endogenous constrictor, unlike relaxing signals such as nitric oxide.
Calcium-induced calcium release: A process in which calcium entering a cell triggers further calcium release from intracellular stores. In vascular muscle, rising intracellular calcium helps initiate contraction.
Blood pressure: The force exerted by circulating blood against the walls of blood vessels. Constriction can raise pressure upstream by increasing resistance.

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