Final answer:
Innate immunity is an individual's natural defense system that operates through physical barriers like skin and mucous membranes, as well as physiological responses involving various immune cells and substances.
Step-by-step explanation:
Innate immunity refers to the set of defense mechanisms present at birth that act as the first and second lines of defense against pathogens. It includes both physical and physiological responses. The body's first line of defense is comprised of physical barriers such as the skin and mucous membranes, which prevent the entry of pathogens. These barriers are aided by mechanical actions like coughing and flushing of bodily fluids, as well as by a beneficial layer of microbiota that competes with pathogens.
The body's second line of defense is characterized by rapid, nonspecific responses that involve a range of cells and chemical factors. Key players in this innate immune response include cells such as phagocytes (neutrophils, eosinophils, dendritic cells, and macrophages), and processes like inflammation and fever. Additionally, antimicrobial substances play a crucial role in this defense layer.
If these innate defenses are insufficient, adaptive immunity is activated, which is more specific and can remember pathogens, providing long-term immunity.