The primary function of the subcutaneous tissue (hypodermis) includes:

Correct Answer: D

Rationale: The hypodermis insulates via adipose tissue, reducing heat loss, and stores energy as fat reserves, supporting survival during scarcity. Sweat production and temperature regulation (via vessels) occur in the dermis. The physical barrier is the epidermis's role. Insulation and energy storage define the hypodermis's primary function, cushioning and sustaining the body, making this the correct answer.

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.

Correct Answer: A

Rationale: The epidermis, the outermost skin layer, has specific characteristics that define its role as a protective barrier. It is not highly vascular; it lacks blood vessels entirely, relying on diffusion from the dermis for nutrients. This avascular nature distinguishes it from the dermis, which is rich in blood supply. The epidermis does contain melanin, produced by melanocytes, and keratin, formed as cells mature, both essential for protection and strength. It is distinctly stratified, with layers like the stratum germinativum, spinosum, granulosum, and corneum reflecting its cellular progression. It also gives rise to sebaceous and sweat glands, which develop as epidermal invaginations into the dermis. The false statement is the claim of vascularity, as the epidermis's lack of blood vessels is a fundamental feature, ensuring it remains a tough, renewable barrier while depending on underlying tissues for sustenance, a design critical to its function.