Question

How does the human body protect itself from infection?

Answer 1

1. Protective Surface Barriers: The skin acts as a physical barrier preventing pathogen entry. The mucous membranes lining the respiratory, digestive, and urogenital tracts trap microbes in mucus, which is cleared by ciliary action. Secretions like tears and saliva contain enzymes such as lysozyme that inhibit microbial growth. Acidic environments in the stomach and vagina also help kill or inhibit microbes.
2. Non-specific Cellular Responses: If pathogens bypass surface barriers, the body’s second line of defense includes phagocytic cells like macrophages and neutrophils that engulf and destroy invaders. Infected cells release interferons to inhibit viral replication. Acute inflammation occurs at infection sites, increasing blood flow and immune cell recruitment, leading to redness, swelling, heat, and pain that help contain infections.
3. The Immune System (Specific Immunity): The immune system distinguishes self from non-self and mounts specific responses via lymphocytes. B-lymphocytes produce antibodies targeting specific antigens (humoral immunity), while T-lymphocytes destroy infected cells directly (cellular immunity). Immunity can be innate (non-specific, present at birth) or acquired (specific, with memory) to protect against repeat infections.