Final answer:
The second line of defense in the innate immune system activates when pathogens get past the physical and chemical barriers of the first line, such as through a cut. It includes non-specific responses like the inflammatory response and the action of phagocytes targeting any invading pathogen.
Step-by-step explanation:
After the first line of defense, the innate immune system and its second line of defense take over. This includes mechanisms like the inflammatory response and phagocytosis by nonspecific leukocytes.
Our body's first line of defense employs various physical and chemical barriers like skin, mucus, and stomach acid, akin to a castle's moat and walls, to keep pathogens out. If a pathogen breaches these barriers, say through a cut, it encounters the internal second line of defense which aims to neutralize and eliminate the invader. This response is non-specific, meaning it targets any pathogen rather than a specific one.
This second line includes a variety of internal defense mechanisms tasked with protecting the body against foreign invaders, employing cells and substances that identify and attack pathogens which have penetrated the external barriers.