High-Q | סימולציה 4

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סימולציה מס' 4

– אנגלית פרק שני

Text II (Questions 18-22)

The most common types of allergic reactions - hay fever, some kinds of asthma and hives - are produced when the immune system responds to a false alarm. In a susceptible person, a normally harmless substance - grass pollen or house dust, for example - is perceived as a threat and is attacked. Such allergic reactions are related to the antibody known as immunoglobulin E or IgE. Like other antibodies, each IgE antibody is specific; one reacts against oak pollen, another against ragweed. The role of IgE in the natural order is not known, although some scientists suspect, that it developed as a defence against infection by parasitic worms. The first time an allergy-prone person is exposed to an allergen (a substance capable of causing an allergic reaction), he or she makes large amounts of the corresponding IgE antibody. These IgE molecules attach to the surfaces of mast cells (in tissues), or basophiles (in the circulation). Mast cells are plentiful in the lungs, skin, tongue and linings of the nose and intestinal tract. When an IgE antibody sitting on a mast cell or basophile encounters its specific allergen, the IgE antibody signals the cell to release the powerful chemicals stored within it. These chemicals include histamine, heparin and substances that activate blood platelets and attract additional cells. The activated mast cell or basophile also synthesises new chemical mediators on the spot. It is such chemical mediators that cause the symptoms of allergy, including wheezing, sneezing, runny eyes and itching. They can also produce anaphylactic shock, a life threatening allergic reaction characterized by swelling of body tissues, including the throat and tongue, and a sudden fall in blood pressure.

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Questions

18. What does the passage mainly discuss?

(1) Chemical mediators in the human body (2) The mechanism of allergic reactions (3) Pollen allergy (4) The immune defense system

19. The author mentions grass pollen and house dust (line 3) -

(1) in order to refute a common misconception. (2) as an example of harmless substances that never cause an allergic reaction. (3) as an example of substances which the body may falsely perceive as dangerous. (4) as the most common causes of allergic reactions.

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