What is the primary function of melanocytes in the epidermis?

Correct Answer: C

Rationale: Melanocytes, in the stratum basale, produce melanin pigment, which colors skin and protects against UV radiation by absorbing it, reducing DNA damage. Temperature regulation involves sweat glands and vessels, not melanocytes. Sweat is from sudiferous glands, not pigment cells. Hair follicle nourishment comes from dermal blood and sebum, not melanocytes. Melanin's role in pigmentation and photoprotection, distributed to keratinocytes, defines their primary function, a vital epidermal process.

Correct Answer: A

Rationale: The epidermis contains Langerhans cells, dendritic immune cells in the stratum spinosum, which detect pathogens and initiate immune responses, aiding protection. The dermis has macrophages and mast cells, but the question emphasizes the layer with these cells as a primary feature, pointing to the epidermis's barrier role. The hypodermis (subcutaneous tissue) lacks significant immune cells. The epidermis's immune function, via Langerhans cells, makes it the correct layer.

Correct Answer: B

Rationale: The subcutaneous tissue (hypodermis) is rich in connective tissue, including adipose (fat) and loose areolar tissue, binding skin to underlying structures while cushioning. Muscle tissue is deeper, nervous tissue is sparse (mostly nerves traversing), and epithelial tissue forms the epidermis, not hypodermis. Connective tissue's dominance, supporting fat and vessels, defines its composition, making this the correct type.

Correct Answer: C

Rationale: The integumentary system protects against infection via the skin's barrier (stratum corneum) and immune cells (Langerhans), blocking pathogens. Blood clotting is a circulatory function, digestion is gastrointestinal, and respiration is pulmonary, none integumentary roles. Infection prevention, a core protective task, makes this the correct external factor.