Final answer:
Innate immunity refers to the body's first line of defense against pathogens, which includes skin and mucous membranes as physical barriers. These barriers work continuously to block and expel pathogens through various mechanisms like trapping them in mucus or expelling them with bodily fluids.
Step-by-step explanation:
Immunity refers to the physical barriers that prevent pathogens from entering the body, such as skin and mucous membranes. These physical barriers are part of the body's innate immune system, and include mechanical defenses that physically block pathogens. The skin is considered the most important mechanical barrier and is the body's primary defense mechanism against infectious agents. Other mechanical barriers include mucous membranes, which are covered in sticky mucus that traps pathogens, hairs in the nose that catch larger pathogens, and cilia in the upper respiratory tract that move trapped pathogens out of the body.
These innate defenses are always active, not just in response to an infection, offering continuous protection from a broad range of pathogens. This protection is bolstered by the skin's acidity, beneficial microorganisms that inhabit the skin, the low pH of the stomach, and bodily mechanisms like coughing, peristalsis, and urination that expel pathogens.