Biology - Allergic Reactions
Allergic reactions are overreactions of immune system to antigens. Mast
cells are fixed immune cells containing histamines. Antigen-antibody links
trigger the release of the histamines, causing blood vessels to dilate
(redness, swelling and inflammation); and causing the contraction of smooth
muscle such as that of the bronchi, as in hay fever and asthma.
Some allergic reactions can be severe, as in the case of bee stings.
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