What is the primary function of the integumentary system?

The primary function of the integumentary system is indeed protection and regulation of temperature. The integumentary system, which includes the skin, hair, nails, and associated glands, serves as the body's first line of defense against environmental hazards such as pathogens, UV radiation, and physical injuries. It acts as a barrier that helps prevent water loss and protects underlying tissues from damage.

Additionally, this system plays a crucial role in thermoregulation. The skin helps maintain body temperature through processes like sweating and the dilation or constriction of blood vessels. When body temperature rises, sweat glands produce sweat, which cools the body as it evaporates. Conversely, when it’s cold, blood vessels constrict to conserve heat.

The other options do not pertain to the integumentary system's primary functions. For example, while blood cell production occurs primarily in the bone marrow, hormonal regulation is associated with the endocrine system, and facilitation of movement relates to the muscular and skeletal systems. Thus, the integumentary system’s main roles center around protection and maintaining a stable internal environment through temperature regulation.