A human child is born with certain non-specific defense mechanisms that prevent the entry of pathogens. Which of the following represents a physical barrier of this innate immune system?

Step-by-step solution

Innate immunity consists of four types of barriers: Physical barriers: Skin on our body is the main barrier which prevents the entry of micro-organisms. The mucus coating of the epithelium lining the respiratory, gastrointestinal, and urogenital tracts also helps in trapping microbes entering our body. Physiological barriers: Acid in the stomach, saliva in the mouth, and tears from the eyes prevent microbial growth. Cellular barriers: Certain types of leukocytes (WBC) of our body like polymorphonuclear leukocytes (