vasoconstriction

Examples of vasoconstriction in the following topics:

• Vascular Spasm

  • Vasoconstriction is the narrowing of the blood vessels, which reduces blood loss during injury.
  • During hemostasis, a brief spasm of vasoconstriction occurs, which slows blood flow into the injured area while the clot forms.
  • Vasoconstriction also causes an increase in blood pressure for affected blood vessels.
  • During injury, vasoconstriction is brief, lasting only a few minutes while the platelet plug and coagulation cascade occur.
  • Blood vessel experiencing vasoconstriction as its smooth muscle contracts while the blood clot forms.

• Distribution of Blood

  • Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles.
  • On a larger level, vasoconstriction is one mechanism by which the body regulates and maintains mean arterial pressure.
  • Substances causing vasoconstriction are called vasoconstrictors or vasopressors.
  • The extent of vasoconstriction may be slight or severe depending on the substance or circumstance.
  • The process is essentially the opposite of vasoconstriction.

• Short-Term Chemical Control

  • Vasoconstriction is the narrowing of blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles.
  • Generalized vasoconstriction usually results in an increase in systemic blood pressure, but may also occur in specific tissues, causing a localized reduction in blood flow.
  • The mechanism that leads to vasoconstriction results from the increased concentration of calcium (Ca2+ ions) and phosphorylated myosin within vascular smooth muscle cells.
  • As with vasoconstriction, vasodilation is modulated by calcium ion concentration and myosin phosphorylation within vascular smooth muscle cells.
  • Vasoconstriction of a microvessel by pericytes and endothelial cells that encircle an erythrocyte (E).

• Local Regulation of Blood Flow

  • Blood flow is regulated by vasoconstriction or vasodilation of smooth muscle fibers in the walls of blood vessels, typically arterioles.
  • Local responses to stretch, carbon dioxide, pH, and oxygen also influence smooth muscle tone and thus vasoconstriction and vasodilation.
  • Generally, norepinephrine and epinephrine (hormones secreted by sympathetic nerves and the adrenal gland medulla) are vasoconstrictive, acting on alpha-1-adrenergic receptors.
  • A number of hormones influence arteriole tone such as the vasoconstrictive epinephrine, angiotensin II, and endothelin and the vasodilators bradykinin and prostacyclin.

• Blood Flow in the Skin

  • These muscles are under the control of the sympathetic nervous system and provide an efficient means of thermoregulation through vasoconstriction and vasodilation.
  • When vasoconstricted, blood flow through the skin is reduced, so less core heat is lost.

• Adrenergic Neurons and Receptors

  • Adrenaline (epinephrine) reacts with both α- and β-adrenoceptors, causing vasoconstriction and vasodilation, respectively.
  • The result is that high levels of circulating epinephrine cause vasoconstriction.
  • Common (or still unspecified) effects include: vasoconstriction of cardiac arteries (coronary artery), vasoconstriction of veins, and decreased motility of smooth muscle in the gastrointestinal tract.
  • It causes vasoconstriction in many blood vessels, including those of the skin, gastrointestinal system, kidney (renal artery), and brain.

• Platelet Plug Formation

  • The second critical step in hemostasis, which follows vasoconstriction, is platelet plug formation.
  • Thromboxane is an arachidonic acid derivative (similar to prostaglandins) that activates other platelets and maintains vasoconstriction.
  • Serotonin is a short-lived inflammatory mediator with a vasoconstrictive effect that contributes to vascular changes associated with inflammation during an injury.

• Overview of Hemostasis

  • Hemostasis includes three steps that occur in a rapid sequence: (1) vascular spasm, or vasoconstriction, a brief and intense contraction of blood vessels; (2) formation of a platelet plug; and (3) blood clotting or coagulation, which reinforces the platelet plug with fibrin mesh that acts as a glue to hold the clot together.
  • The vasoconstriction that occurs during hemostasis is a brief reflexive contraction that causes a decrease in blood flow to the area.

• Introduction to Blood Flow, Pressure, and Resistance

  • Arterioles in particular are able to rapidly alter resistance by altering their radius through vasodilation or vasoconstriction.
  • Blood pressure can be modulated through altering cardiac activity, vasoconstriction, or vasodilation.

• Epidermal Wound Healing

  • As the epidermis is itself not vascularised—it is receiving blood from the dermis—a clotting and vasoconstrictive response is often not necessary.