And follow up: why do mine hate me?
In: Biology
histamines are chemicals that are naturally in your body and are released during an immune response, they cause most of the symptoms. They don’t hate you. They love you and just want to protect you from the horrendous parasites that are definitely attacking you disguised as harmless pollen or cat spit.
Histamine is a molecule that’s involved in Tbh a lot more than you’d expect.
In the case of immune function, histamine is produced by mast cells (a type of immune cell). When a specific kind of antibody known as IgE antibodies bind to an antigen, they trigger mast cells to release histamine. In this scenario, histamine triggers inflammation and vasodilation. IgE antibodies are typically associated with defense against parasites, and allergies are essentially when something is improperly labeled as a pathogen and you have IgE antibodies in production against it. It’s also involved in bronchoconstriction and inflammation in asthma.
Histamine is also produced in the hypothalamus in the brain where it acts as a neurotransmitter and is associated with regulation of the sleep wake cycle. This is why 1st generation antihistamines (such as diphenhydramine aka Benadryl), which are capable of crossing the blood-brain-barrier, cause drowsiness. 2nd generation antihistamines (Claritin, Zyrtec, Allegra, etc) were largely made to avoid this but some still can even if very rarely.
In the stomach, there are enterochromaffin-like cells (which are also neuroendocrine cells) that produce and secrete histamine, which leads to the secretion of stomach acid. But this isn’t the only mechanism so an antihistamine for this scenario is effective for reducing nocturnal stomach acid secretion with only a modest effect on meal stimulated acid.
Do note that allergies and the drowsiness are mediated by H1 histamine receptors and the stomach acid secretion is mediated by the H2 histamine receptor. This is why allergy medications don’t have an effect on stomach acid and why H2 antihistamines used for gastric ulcers/acid reflux and wouldn’t affect allergies.
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