What is the primary role of sweat glands in the skin?

Correct Answer: A

Rationale: Sweat glands, primarily eccrine, regulate body temperature by secreting sweat, which evaporates to cool the skin, a key thermoregulatory mechanism. Melanin production is melanocytes' job, not glands'. Hair follicle nourishment involves blood vessels and sebum, not sweat. Joint lubrication is synovial fluid's role, not skin-related. Sweat glands' production of water and electrolytes, triggered by heat or exercise, directly supports homeostasis by dissipating heat, making temperature regulation their primary function, widely recognized in physiology.

Correct Answer: D

Rationale: Vitamin D synthesis occurs in the skin when UV light converts 7-dehydrocholesterol in the epidermis to previtamin D3, essential for calcium absorption. Thermoregulation uses sweat and vessels, sensation involves receptors, and excretion removes waste via sweat, none involving UV-driven synthesis. This photochemical process, unique to skin, distinguishes vitamin D production as a key function, making it the correct answer.

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.