Synthesizes vitamin D, and houses cutaneous receptors and sweat and oil glands.

• A. Integumentary system
• B. Endocrine system
• C. Digestive system
• D. Respiratory system

Answer: (A)

The skin’s functions include vitamin D synthesis and hosting sensory and exocrine structures, which is why the integumentary system is the correct choice. When skin is exposed to UVB light, a cholesterol derivative in the epidermis is converted to previtamin D3 and then becomes active vitamin D after further processing in the liver and kidneys. The skin also houses cutaneous receptors that detect touch, pressure, temperature, and pain, providing protective feedback and sensation. Sweat glands help regulate body temperature, while sebaceous glands produce oil to keep skin and hair moisturized and protected. These roles are specific to the skin and don’t align with the primary duties of the endocrine, digestive, or respiratory systems.