|Class 12 Biology Human Health Disease||Immunity|
The overall ability of the body to fight against disease causing microorganisms with the help of immune system is called immunity.
Immunity is of two types-
1. Innate immunity.
2. Acquired immunity.
The immunity which occurs by birth is called innate immunity.
Innate immunity is non-specific type of defense.
Innate immunity consists of various barriers which prevent the entry of microorganisms into the body.
Innate immunity consists of four types of barriers.
The immunity which develops during lifetime by exposure to suitable foreign agents like microorganisms is called acquired immunity.
Acquired immunity is pathogen specific and it ischaracterized by memory.
When the body first encounters a pathogen it produces a response which takes long time to develop and of low intensity called as primary immune responseand if the body encounters the same pathogen it produces highly intensified and quick response called as secondary immune response.
After responding to the foreign microorganisms and elimination of the pthogen, the immune system keeps the memory of the that encounter (primary response) and during its second encounter with the same pathogen produces a highly intensified immune response (secondary response).
The primary and secondaryimmune responses are carriedout with the help of twospecial types of lymphocytes present in our blood,
Fig. B-lymphocyte and T-lymphocyte