American Academy of Professional Coders (AAPC) 2026 – 400 Free Practice Questions to Pass the Exam

The integumentary system functions as the body's first line of defense against harmful microorganisms, such as bacteria, viruses, and fungi. This function is primarily achieved through the physical barrier created by the skin, which acts to keep pathogens out. The epidermis (the outermost layer of the skin) has tightly packed cells that create a formidable barrier, reducing the likelihood of infection.

Additionally, the skin produces antimicrobial substances, such as defensins and other proteins, that help neutralize potential threats. This protective role is vital in maintaining the body's overall health and preventing the entry of infectious agents.

While fluid balance, temperature regulation, and fluid loss are important functions of the integumentary system, they primarily relate to maintaining homeostasis rather than directly providing a protective barrier against microorganisms. Hence, the option highlighting protection from injury encapsulates the chief aspect of safeguarding against infections and other external invaders.