What is one difference between the dermis and the epidermis? The

Correct Answer: D

Rationale: The dermis is vascularized, with blood vessels supplying nutrients, while the epidermis is avascular, relying on diffusion from dermal capillaries. The epidermis is epithelial cells, not connective tissue (dermis has that). The dermis isn't exterior (epidermis is) and is part of the skin, not excluded. Vascularity's contrast epidermis lacking vessels, dermis rich with them defines their structural and functional difference, making this the accurate distinction.

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: 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: 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.