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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.
A mast cell (also known as a mastocyte or a labrocyte [1]) is a resident cell of connective tissue that contains many granules rich in histamine and heparin.Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a part of the immune and neuroimmune systems.
Endogenous substances and drugs that cause vasodilation are termed vasodilators. Many of these substances are neurotransmitters released by perivascular nerves of the autonomic nervous system [ 6 ] Baroreceptors sense blood pressure and allow adaptation via the mechanisms of vasoconstriction or vasodilation to maintain homeostasis .
Chemical factors produced during inflammation (histamine, bradykinin, serotonin, leukotrienes, and prostaglandins) sensitize pain receptors, cause local vasodilation of the blood vessels, and attract phagocytes, especially neutrophils. [5]
The histamine receptors are a class of G protein–coupled receptors which bind histamine as their primary endogenous ligand. [ 1 ] [ 2 ] Histamine receptors are proteins that bind with histamine, a neurotransmitter involved in various physiological processes.
Vasodilation and its resulting increased blood flow causes the redness (rubor) and increased heat (calor). Increased permeability of the blood vessels results in an exudation (leakage) of plasma proteins and fluid into the tissue ( edema ), which manifests itself as swelling ( tumor ).
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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: