Final answer:
The body's first line of defense against pathogens includes mechanical barriers like skin and mucous membranes, chemical barriers such as tears and saliva, and biological barriers like friendly bacteria. These defenses are non-specific, designed to block all pathogens, and are supported by the innate immune system.
Step-by-step explanation:
The first line of cellular defense against pathogens comprises mechanical, chemical, and biological barriers that work together to protect the body from infectious agents. These barriers are non-specific, meaning they aim to prevent any pathogen from entering the body. Pathogens include bacteria, viruses, and other microorganisms that can cause disease.
Physical and Chemical Barriers
The skin and mucous membranes serve as mechanical barriers, whereas tears, saliva, and stomach acid are examples of chemical barriers that destroy pathogens. Inflammation and the secretion of immune factors bolster these defenses if pathogens manage to bypass the initial barriers.
Biological Barriers and Innate Immune System
Friendly bacteria act as biological barriers, competing with pathogens for resources and space. The innate immune system, consisting of cells such as natural killer cells, macrophages, and mast cells, stands ready to react to pathogens that defeat the first line of defense. Proteins like complement and interferon also play a crucial role in the body's immune response.