Which system is described as the largest organ of the body?

The integumentary system is referred to as the largest organ of the body because it comprises the skin, which is the body's outer protective layer. The skin plays a vital role in shielding the internal organs from external pathogens, regulating body temperature, and providing sensory information through its various receptors.

While other systems, such as the muscular and circulatory systems, include numerous organs and components, they do not comprise a single cohesive structure as the skin does. The nervous system, although extensive in neural connections and distribution throughout the body, does not encompass the size or protective function of the integumentary system. Thus, the integumentary system's unique characteristics, including its extensive coverage and multifunctional role, solidify its position as the largest organ of the body.