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It has been known for more than one hundred years that an intravenous injection of histamine causes a fall in the blood pressure. [30] The underlying mechanism concerns both vascular hyperpermeability and vasodilation. Histamine binding to endothelial cells causes them to contract, thus increasing vascular leak.
Anaphylactic shock is caused by a severe anaphylactic reaction to an allergen, antigen, drug, or foreign protein causing the release of histamine which causes widespread vasodilation, leading to hypotension and increased capillary permeability. Signs of anaphylaxis Signs typically occur after exposure to an allergen and may include:
Vasodilation is also a major component of anaphylaxis. [12] Inflammation causes not only vasodilation but also causes increased vascular permeability, allowing neutrophils, complement proteins, and antibodies to reach the site of infection or damage. [7]
Vasodilation and increased permeability of capillaries are a result of both H1 and H2 receptor types. [34] Stimulation of histamine activates a histamine (H2)-sensitive adenylate cyclase of oxyntic cells, and there is a rapid increase in cellular [cAMP] that is involved in activation of H+ transport and other associated changes of oxyntic cells ...
The main factor involved in causing vasodilation is histamine. [3] [15] Histamine also causes blood vessels to become porous, allowing the tissue to become edematous because proteins from the bloodstream leak into the extravascular space, which increases its osmolar load and draws water into the area. [3]
Once released, the histamine can react with local or widespread tissues through histamine receptors. [citation needed] Histamine, acting on H 1-receptors, produces pruritus, vasodilation, hypotension, flushing, headache, bradycardia, bronchoconstriction, increase in vascular permeability and potentiation of pain. [2]
In vasodilatory shock, the blood vessels are too relaxed leading to extreme vasodilation and blood pressure drops and blood flow becomes very low. Without enough blood pressure, blood and oxygen will not be pushed to reach the body's organs. If vasodilatory shock lasts more than a few minutes, the lack of oxygen starts to damage the body's ...
Anaphylactic shock is associated with systemic vasodilation that causes low blood pressure which is by definition 30% lower than the person's baseline or below standard values. [ 17 ] Biphasic anaphylaxis is the recurrence of symptoms within 1–72 hours after resolution of an initial anaphylactic episode. [ 40 ]