What is the largest organ system in the body?

The integumentary system is the largest organ system in the body, primarily composed of the skin, which is the body's outermost protective layer. Skin serves a variety of essential functions, including protection against environmental hazards, regulation of temperature, sensation, and the synthesis of vitamin D. Since the skin covers the entire body and includes various structures such as hair, nails, and glands, it encompasses a significant surface area, making it the largest organ system.

In contrast, the circulatory, respiratory, and nervous systems are vital systems in the body but do not encompass as extensive an area as the integumentary system. The circulatory system is responsible for the transportation of blood and nutrients, the respiratory system manages gas exchange, and the nervous system controls and coordinates body functions through nerve signals. While these systems are crucial for maintaining overall health and homeostasis, they do not have the same sheer physical size or coverage as the integumentary system. Therefore, the integumentary system is recognized as the largest organ system in the body.