To which category do saliva in the mouth, tears from eyes, and stomach acid belong as protective barriers?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Physiological barriers
Innate immunity works through four types of barriers: physical, physiological, cellular and cytokine barriers. Acid in the stomach, saliva in the mouth and tears from the eyes all prevent microbial growth, and these are grouped as physiological barriers.
Option (1) Cytokine barriers — Incorrect. Cytokine barriers are the interferons, proteins secreted by virus-infected cells. They protect non-infected cells from further viral infection.
Option (2) Cellular barriers — Incorrect. Cellular barriers are leukocytes such as PMNL-neutrophils, monocytes and natural killer cells in the blood, and macrophages in tissues, which phagocytose and destroy microbes.
Option (3) Physiological barriers — Correct. Saliva, tears and stomach acid are physiological barriers. They do not block the entry of microbes; they prevent their growth.
Option (4) Physical barriers — Incorrect. Physical barriers are the skin and the mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts. They stop microbes at entry or hold them in mucus.
NCERT Extract:
Innate Immunity – “… Innate immunity consist of four types of barriers. These are — (i) Physical barriers : Skin on our body is the main barrier which prevents entry of the micro-organisms. Mucus coating of the epithelium lining the respiratory, gastrointestinal and urogenital tracts also help in trapping microbes entering our body. (ii) Physiological barriers : Acid in the stomach, saliva in the mouth, tears from eyes–all prevent microbial growth. (iii) Cellular barriers : Certain types of leukocytes (WBC) of our body like polymorpho-nuclear leukocytes (PMNL-neutrophils) and monocytes and natural killer (type of lymphocytes) in the blood as well as macrophages in tissues can phagocytose and destroy microbes. (iv) Cytokine barriers : Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infection.”