Overview
Immunity is the defense of the body against pathogens, and it has two linked parts: fast, non-specific innate immunity and slower, specific adaptive immunity with memory. This topic covers both and the features of the immune response.
Innate immunity: external barriers
- Immunity refers to the body’s ability to resist and fight against harmful pathogens.
- It is a complex defense system that prevents pathogens from entering the body and eliminates them if they do.
- The immune system includes specialized organs, cells, and molecules working in harmony to maintain health.
- Innate immunity is the body’s natural, non-specific defense mechanism present from birth.
- It does not target specific pathogens but responds broadly to any invader.
- This type of immunity does not improve with repeated exposure to the same pathogen.
- The innate immune response is very fast, usually activated within minutes to a few hours of infection.
Physical Barriers
- The skin acts as a tough physical shield that pathogens cannot easily cross.
- Tears, saliva, and urine mechanically flush out microbes from body surfaces.
- The respiratory tract uses mucociliary clearance where cilia push mucus filled with trapped particles toward the throat to be expelled or swallowed.
Chemical Barriers
- The acidic environment of the stomach and vagina kills many pathogens.
- Lysozymes in saliva, tears, and other secretions break down bacterial cell walls.
- Sudden pH changes from the stomach to the intestines act as additional hostile conditions for microbes.
Biological Barriers
- The body’s natural microbiota (such as gut and vaginal flora) compete with pathogens for space and resources, preventing their colonization.
- These resident microbes may also secrete substances that are toxic to pathogens.
Disruption of Barriers
- Conditions like cystic fibrosis or primary ciliary dyskinesia impair mucociliary clearance, leading to chronic respiratory infections.