What serves as the first layer of defense in the immune system?

The first layer of defense in the immune system is comprised of physical barriers. These barriers serve as the initial point of contact between the body and potential pathogens or harmful entities. Physical barriers include skin and mucous membranes, which prevent the entry of bacteria, viruses, and other intruders.

The skin acts as a robust protective layer, while mucous membranes line the respiratory, gastrointestinal, and urogenital tracts, trapping pathogens and foreign particles. These barriers not only physically block pathogens but also provide an environment that is often inhospitable to their survival.

In contrast, innate passive immunity and adaptive acquired immunity refer to different aspects of the immune response that develop after a pathogen has breached these physical barriers. Cellular responses are part of the immune system's mechanisms that come into play after the initial defenses have been compromised. Understanding the role of these physical barriers is vital for recognizing how the body initially protects itself against infection.