Three functions of the skin are to:

Correct Answer: D

Rationale: Skin functions include producing melanin (via melanocytes) for UV protection, secreting sebum (via sebaceous glands) to lubricate, and minimizing water loss via the stratum corneum's barrier. Storing fat occurs in the hypodermis, not skin. Bile excretion is a liver function, not skin. Keratin production and immunity (via Langerhans cells) are true, but lymphocytes are made in lymphoid organs, not skin. The trio of melanin, sebum, and water retention reflects core integumentary roles, making this the accurate set.

Correct Answer: B

Rationale: The epidermis is the outermost skin layer, encompassing sublayers like the stratum corneum, serving as the body's primary barrier. The dermis lies beneath it, supporting with connective tissue and glands. The stratum lucidum is an epidermal sublayer below the corneum in thick skin. The reticular dermal layer is deep in the dermis. As the topmost structure, the epidermis literally 'over the dermis' is the correct outermost layer, per standard skin anatomy.

Correct Answer: A

Rationale: Skin waterproofs via the stratum corneum, produces vitamin D with UV exposure, and aids immunity via Langerhans cells, but fat storage occurs in the hypodermis (subcutaneous layer), not the integument (epidermis and dermis). The hypodermis's role in energy storage is distinct from skin functions, which focus on protection, synthesis, and sensation. Fat storage's exclusion from the integument proper, per anatomical definition, makes this the non-function.

Correct Answer: A

Rationale: Merkel discs (touch), nociceptors (pain), and Pacinian corpuscles (pressure) are sensory receptors in the skin, detecting environmental stimuli. The reticular dermal layer, the deeper dermis part, is connective tissue with collagen and elastin, not a receptor. It supports receptors but doesn't sense, distinguishing it from the others, which are specialized nerve endings or structures, making it the non-receptor.

Correct Answer: B

Rationale: Sebaceous glands, located in the dermis, primarily produce sebum, an oily substance that lubricates skin and hair, preventing dryness and aiding waterproofing. Sweat production is the role of sudiferous glands (eccrine and apocrine), not sebaceous. Melanin comes from melanocytes in the epidermis, not glands. Collagen is synthesized by fibroblasts in the dermis, not secreted by glands. Sebum's lipid-rich composition, secreted into hair follicles, distinguishes sebaceous glands' function, essential for skin and hair maintenance, making this the accurate primary role.