Lesson 5 of 13 · 6 min
Innate immunity
NCERT §7.2, §7.2.1
Nikhil notices that the nurses, who meet sick people all day, are mostly well. Dr Leela says the body is fighting germs every minute, and most of the time it wins before we notice.
The lesson in notes
In short
We meet infectious agents every day, yet only a few exposures cause disease, because the body defends itself. The host's overall ability, given by the immune system, to fight disease-causing organisms is immunity.
Immunity is of two types: innate and acquired.
Innate immunity is non-specific and present at birth. It works through four types of barriers to foreign agents.
Physical barriers: the skin is the main one. Mucus coating the epithelium of the respiratory, gastrointestinal and urogenital tracts traps entering microbes.
Physiological barriers: stomach acid, saliva in the mouth and tears from the eyes all stop microbes from growing.
Cellular barriers: in blood, polymorpho-nuclear leukocytes (PMNL-neutrophils), monocytes and natural killer cells (a type of lymphocyte), and in tissues, macrophages, can phagocytose and destroy microbes.
Cytokine barriers: a cell infected by a virus releases proteins called interferons, which shield the cells around it that are not yet infected.