Final answer:
Innate immunity is the type of immunity that is present at birth and operates without prior exposure to pathogens. It differs from adaptive immunity, which develops after exposure and involves immunological memory. Innate immunity provides immediate, non-specific defense against a broad range of pathogens.
Step-by-step explanation:
The type of immunity that is fully functional without previous exposure to various foreign invaders is known as innate immunity. Unlike adaptive immunity, which develops after exposure to a specific pathogen and involves a memory component, innate immunity is present from birth and does not require prior exposure to function effectively. Innate immune responses are quick and general, targeting a wide range of pathogens through a consistent sequence of events. This form of immunity includes physical barriers like the skin and mucous membranes, as well as immune cells that respond to pathogens in a generic rather than a specialized manner.
Adaptive immunity, on the other hand, refers to the acquired defense mechanisms that involve specific responses to particular antigens. After an initial exposure to a pathogen, adaptive immunity leads to the creation of memory lymphocytes (B or T cells), which provide a stronger and faster response upon subsequent exposures. This process is known as immunological memory and underlies the body's ability to resist reinfection by the same pathogen.
In short, while adaptive immunity requires time and exposure to develop, innate immunity is immediate and universally present, acting as the first line of defense against pathogens.