Which system protects the body from harm such as fluid loss and infection?

The integumentary system is the body's first line of defense against external threats, including fluid loss and infections. This system comprises the skin, hair, nails, and various glands. The skin, specifically, serves several vital functions: it acts as a barrier that prevents pathogens from entering the body, protects internal organs from injury, helps regulate body temperature, and minimizes fluid loss through its ability to form a watertight covering.

The multiple structures within the integumentary system, particularly the skin's layers (epidermis, dermis, and subcutaneous tissue), play crucial roles in these protective functions. For instance, the epidermis contains cells that form a tough barrier and produce antimicrobial substances, while the dermis houses immune cells that help in the detection of potential infections.

Other systems listed, such as the nervous system, endocrine system, and musculoskeletal system, have roles in the body, but they do not primarily serve the purpose of protecting against fluid loss and infections in the same direct and essential way that the integumentary system does. The nervous system primarily facilitates communication and coordination within the body, the endocrine system regulates hormones and metabolic processes, while the musculoskeletal system supports body structure and movement. Therefore, the integumentary system is