Which layer of the skin is the most superficial?

Correct Answer: A

Rationale: The epidermis is the outermost skin layer, encompassing sublayers like the stratum corneum and germinativum, serving as the body's protective shield. The dermis lies beneath it, with the papillary dermal layer as its upper part, still deeper than the epidermis. The stratum germinativum (basale) is the deepest epidermal sublayer, not the most superficial. As a whole, the epidermis sits atop the dermis, making it the most superficial layer in skin anatomy, consistent with its role as the first barrier to the environment.

Correct Answer: A

Rationale: Melanocytes in the stratum basale produce melanin, the pigment that darkens skin (tanning) upon sunlight exposure, absorbing UV to protect cell nuclei. Keratinocytes form keratin, not pigment, though they receive melanin. Dendrocytes (likely dendritic cells) handle immunity, not tanning. Lymphocytes, immune cells, aren't skin-based or pigment-related. Melanocytes' UV-responsive melanin production is the mechanism behind tanning, a protective adaptation, making them the correct cell type.

Correct Answer: B

Rationale: Keratin, a fibrous protein in the epidermis, fills the stratum corneum's dead cells, protecting against abrasion by forming a hard, renewable barrier. Melanin is a pigment for UV protection, not abrasion. Sebum is an oily secretion, not fibrous. Elastin, in the dermis, provides elasticity, not abrasion resistance. Keratin's toughness, shed and replaced as skin wears, is the key anti-abrasion mechanism, widely recognized in skin structure.

Correct Answer: D

Rationale: The skin is the largest organ in the human body, covering an average surface area of about 1.5 to 2 square meters in adults and weighing approximately 4-5 kilograms, including the epidermis, dermis, and hypodermis. It surpasses the heart, liver, and lungs in both size and mass when considered as a whole organ system. The heart, though vital, is a small muscular organ, roughly 300 grams. The liver, at about 1.5 kilograms, is significant but smaller in surface area. The lungs, while expansive internally, have a combined weight of around 1 kilogram and less external coverage than skin. The skin's extensive role in protection, sensation, and thermoregulation, coupled with its sheer physical extent across the body, confirms it as the largest organ, a fact well-established in anatomy.

Correct Answer: D

Rationale: Arrector pili muscles, small smooth muscles in the dermis attached to hair follicles, contract under sympathetic nervous stimulation (e.g., cold or fear), pulling hairs upright and causing goosebumps (piloerection). They don't sense temperature thermoreceptors do that. Melanin is from melanocytes, not muscles. 'Ejecting hair shafts' isn't a function; hairs grow or shed via follicles, not muscle action. Goosebumps, an evolutionary remnant to trap air or signal emotion, define their primary role, per skin anatomy.