Following the rule of nines. What percent would a third degree burn to the entire arm and back cover?

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: 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.

Correct Answer: C

Rationale: Alopecia, or hair loss, has multiple potential causes, but one predominates. Protein deficiencies can weaken hair, as keratin requires amino acids, but this is rare in well-nourished populations and not the leading cause. Dermal viral infections might cause localized hair loss (e.g., fungal infections like ringworm), but they are not primary alopecia triggers. Stress can induce temporary hair loss (telogen effluvium), where hair follicles enter a resting phase, but it's reversible and less common as a chronic cause. Genetic inheritance, particularly androgenetic alopecia (male or female pattern baldness), is the most probable and widespread cause, affecting millions globally. Driven by hormones (androgens) and genetics, it leads to progressive follicle miniaturization. Studies show its prevalence up to 50% of men and 25% of women by age 50 outstrips other causes. Its permanence and familial patterns distinguish it as the dominant etiology, aligning with clinical observations and epidemiological data.

Correct Answer: C

Rationale: The arrector pili are small muscles attached to hair follicles, controlled by the sympathetic nervous system. When stimulated (e.g., by cold or fear), they contract, pulling the hair upright and causing the skin to pucker, resulting in goose bumps (piloerection). They are not glands, so they don't secrete anything like sebum (which comes from sebaceous glands) or sweat (from sweat glands). Excessive sweating is linked to eccrine glands, not arrector pili. Their role in creating goose bumps is a well-known physiological response to sympathetic activation, conserved from animals raising fur for warmth or defense, making this the correct function.