NCERT · Class 12 · Biology · Human Health and DiseasesExplain the four types of innate immunity barriers present in the human body that prevent the entry of pathogens.

Innate immunity is a non-specific type of defense present at the time of birth. It consists of four main types of barriers:

1. Physical Barriers: The skin on our body is the primary barrier that prevents the entry of microorganisms. Mucous membranes coating the lining of the respiratory, gastrointestinal, and urogenital tracts also trap microbes entering our body.
2. Physiological Barriers: Acid in the stomach, saliva in the mouth, and tears from the eyes contain anti-microbial components (such as lysozyme) that prevent microbial growth.
3. Cellular Barriers: Certain leukocytes (white blood cells) such as polymorphonuclear leukocytes (PMNL-neutrophils), monocytes, and natural killer (type of lymphocytes) in the blood, as well as macrophages in tissues, can phagocytose and destroy microbes.
4. Cytokine Barriers: Virus-infected cells secrete proteins called interferons, which protect non-infected cells from further viral infection.