CBSE Class 9 Answered

During infection, the immune system gets activated. It sends many soldier cells to the affected tissue to kill the microbes. This causes inflammation.

Inflammation or oedema is due to the escape of some chemicals such as histamine and 5′-hydroxytrptoamine from the damaged tissues. These chemicals cause allergic reactions in our body. They attract blood supply due to which the amount of blood and the temperature of the surrounding area increase. The consequent swelling of the area is called oedema.

Plasma and white blood cells (WBCs) of the immune system of the body are discharged at the affected site. The plasma contains products such as antibodies and macrophages which kill or inhibit the growth of pathogens.