Which layer of the integument contains rapidly dividing keratinocytes?

Correct Answer: C

Rationale: The stratum germinativum, also called the stratum basale, is the deepest epidermal layer where keratinocytes rapidly divide via mitosis to replenish the epidermis, replacing cells lost from the surface. The stratum lucidum, in thick skin, is a thin, dead layer above the basale, not dividing. The papillary and reticular dermal layers are in the dermis, containing connective tissue, not keratinocytes. The germinativum's name (from 'germinate') reflects its role as the regenerative base, a key feature of epidermal renewal confirmed by histological studies.

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: C

Rationale: Transdermal administration means a drug is absorbed through the skin into the bloodstream for systemic effects (e.g., nicotine patches), not just local action (topical). Injection into the dermis is intradermal, and into subcutaneous fat is hypodermic, both distinct from surface application. 'Trans' indicates crossing the skin barrier, requiring penetration of the stratum corneum to reach circulation, a method reliant on skin permeability, making systemic action the defining feature.

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.