What happens during mast cell degranulation?
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antihistamine
Antihistamines such as Benadryl (diphenhydramine) and Claritin (loratadine) can be purchased without prescriptions. Both of those agents act by blocking H1 receptors. However, whereas Benadryl binds to those receptors in the central nervous system (CNS), causing drowsiness, Claritin does not readily enter the CNS and thus does not normally cause drowsiness.
During mast cell degranulation, mast cellsâwhich are immune system cells found in connective tissuesâare stimulated by an allergen or antigen. This stimulation causes the cells to release the contents of their coarse cytoplasmic granules into the surrounding tissues.12
These granules contain various chemical mediators, most notably histamine, as well as interleukins, proteoglycans like heparin, and enzymes. Once released, these mediators trigger local inflammatory responses, including:12
- Vascular changes: Dilation of blood vessels and increased permeability, which leads to tissue swelling and allows immune cells to migrate to the site of injury.12
- Muscle contraction: Constriction of smooth muscles, such as those in the bronchi.12
- Secretory effects: Increased mucus production and stimulation of gastric acid secretion.12
In the context of an allergic reaction, this process occurs in excess, resulting in symptoms like runny nose, watery eyes, and, in severe cases, anaphylaxis.2