What is the primary function of the arrector pili muscles in the skin?

• A. To protect the skin from UV rays
• B. To cause hair to stand upright
• C. To produce sweat
• D. To absorb nutrients

Answer: (B)

The primary function of the arrector pili muscles in the skin is to cause hair to stand upright. These tiny, smooth muscles are attached to hair follicles, and when they contract, they pull the hair follicles into an upright position, which is often observed as "goosebumps." This reaction is part of the body's response to cold temperatures or emotional stimuli, allowing trapped air to create an insulating layer over the skin and providing some thermal regulation. Furthermore, this response can also signal aggression or fear in animals by making them appear larger to potential threats.

Other choices such as protecting the skin from UV rays, producing sweat, and absorbing nutrients do not relate to the specific function of arrector pili muscles. Protection from UV rays is primarily managed by melanin and other skin structures, sweat production is handled by sweat glands, and nutrient absorption typically occurs in the gastrointestinal tract rather than the skin.