Final answer:
An acute reaction caused by ingestion or injection of a sensitizing agent describes an allergy, which is a type of immediate hypersensitivity (type I) response in the immune system. This response occurs within minutes of exposure to an allergen and involves the release of chemical mediators from mast cells, resulting in allergic symptoms.
Step-by-step explanation:
An acute reaction caused by ingestion or injection of a sensitizing agent is known as an allergy. It is a type of immediate hypersensitivity (type I) that occurs within minutes of exposure to a usually harmless antigen.
During the first exposure to the allergen, the immune system produces IgE antibodies that sensitize mast cells in the body. Upon subsequent exposure, the IgE antibodies on mast cells bind to the antigen, causing mast cell degranulation and the release of chemical mediators like histamine.
These chemical mediators can lead to various symptoms, ranging from mild (sneezing, itchy eyes) to severe (hives, airway constriction, anaphylactic shock). Common allergens include animal dander, pollen, insect venom, and certain foods.