Which skin function involves the production of oil (sebum) to moisturize and protect the skin and hair?

Correct Answer: C

Rationale: Lubrication and protection involve sebum production by sebaceous glands, moisturizing skin and hair while adding a protective layer against microbes and dryness. Thermoregulation uses sweat, sensation involves receptors, and vitamin D synthesis uses UV, none tied to oil. Sebum's role in maintaining skin integrity and suppleness defines this function, making it the correct answer.

Correct Answer: C

Rationale: The epidermis is primarily keratinocytes, stratified epithelial cells that produce keratin, forming its layers from basale to corneum, about 90% of its composition. Fibroblasts are dermal, melanocytes produce melanin (a minority), and sebocytes (in sebaceous glands) are dermal, not epidermal. Keratinocytes' dominance and barrier role define the epidermis, making them the correct cell type.

Correct Answer: B

Rationale: The rule of nines estimates body surface area (BSA) for burns in adults: each arm is 9% (front and back), and the back is 18% (posterior torso). A third-degree burn to the entire arm (9%) and the entire back (18%) totals 9 + 18 = 27%. The options include 28%, 27%, 20%, and 18%, and 27% matches the calculation exactly. The rule of nines is a standardized method used in emergency settings to quickly assess burn extent, and here it clearly points to 27% for one arm and the back, confirming this as the correct percentage.

Correct Answer: A

Rationale: Skin cells synthesize vitamin D from 7-dehydrocholesterol (often shortened to dehydrocholesterol) in the epidermis when exposed to UVB light, converting it to cholecalciferol (vitamin D3). Cholesterol is a related lipid but not the direct precursor in this process. Hydrocholesterol and hydrodermis are not real terms in this context; they seem to be distractors. Dehydrocholesterol is specifically stored in the skin and transformed by sunlight, making it the correct substance involved in vitamin D production.

Correct Answer: B

Rationale: During embryonic development, the integumentary system, which includes the skin and its derivatives like hair and nails, originates from specific germ layers. The epidermis, the outermost layer of skin, arises from the ectoderm, which is the outermost embryonic layer responsible for forming external structures. The dermis, the underlying layer of skin, develops from the mesoderm, the middle germ layer that gives rise to connective tissues, muscles, and blood vessels. The endoderm, which forms internal structures like the digestive tract, does not contribute to the integument. Therefore, the correct developmental origin involves only the ectoderm and mesoderm. This dual origin explains the skin's diverse functions: the ectoderm-derived epidermis provides a protective barrier, while the mesoderm-derived dermis supports it with blood vessels, nerves, and connective tissue. Misincluding the endoderm or excluding one of the correct layers would misrepresent the embryological process, making the combination of ectoderm and mesoderm the accurate description of integumentary development.