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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:
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 ...
Histamine has two basic centres, namely the aliphatic amino group and whichever nitrogen atom of the imidazole ring does not already have a proton. Under physiological conditions, the aliphatic amino group (having a pK a around 9.4) will be protonated, whereas the second nitrogen of the imidazole ring (pK a ≈ 5.8) will not be protonated. [11]
Histamine intolerance is a presumed set of adverse reactions (such as flush, itching, rhinitis, etc.) to ingested histamine in food. The mainstream theory accepts that there may exist adverse reactions to ingested histamine, but does not recognize histamine intolerance as a separate medical condition that can be diagnosed. [1]
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]
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Histamine also promotes angiogenesis. [6] Antihistamines suppress the histamine-induced wheal response (swelling) and flare response (vasodilation) by blocking the binding of histamine to its receptors or reducing histamine receptor activity on nerves, vascular smooth muscle, glandular cells, endothelium, and mast cells.
Antihistamines can alleviate some of the milder symptoms of an allergic reaction, but do not treat all symptoms of anaphylaxis. [88] Antihistamines block the action of histamine, which causes blood vessels to dilate and become leaky to plasma proteins. Histamine also causes itchiness by acting on sensory nerve terminals.