Which system includes the skin, hair, nails and acts as a barrier against infection?

• A. Dermis
• B. Subcutaneous Layer
• C. Cartilage
• D. Integumentary System

Answer: (D)

The integumentary system. It includes skin, hair, and nails and acts as the body's first line of defense against infection. The outer skin layer (epidermis) forms a tough physical barrier with keratinized cells in the stratum corneum, held together by junctions that keep microbes out. Chemical defenses, like the slightly acidic surface, sebum, and antimicrobial peptides, further inhibit microbial growth. Immune cells in the skin, such as Langerhans cells, help detect invaders and summon immune responses. Hair and nails are epidermal derivatives that contribute to protection, while the underlying dermis provides structural support and houses vessels and nerves.