Which one of the following cell types is responsible for forming the skin's stratum corneum?

Correct Answer: B

Rationale: Keratinocytes, originating in the stratum basale, migrate upward, producing keratin and dying to form the stratum corneum, the dead, keratin-filled outer layer. Melanocytes produce melanin, not the corneum's structure. Dendrocytes (dendritic cells) are immune-related, not structural. Lymphocytes are in blood or lymph, not forming skin layers. Keratinocytes' differentiation into the corneum's protective barrier is a core epidermal process, making them the responsible cell type.

Correct Answer: C

Rationale: Melanin, produced by melanocytes in the stratum basale, is the pigment responsible for skin color, ranging from light to dark tones, and absorbs UV radiation to protect underlying cells from DNA damage. Melatonin, a hormone from the pineal gland, regulates sleep, not skin color. Hemoglobin, in red blood cells, gives a pinkish hue via dermal blood vessels but isn't a skin pigment or UV shield. Collagen, a dermal protein, provides structure, not pigmentation or UV protection. Melanin's dual role in coloration and photoprotection, darkening with UV exposure (tanning), makes it the correct pigment, per dermatological understanding.

Correct Answer: A

Rationale: The epidermis grows hair and nails via specialized structures: hair from follicles' matrix cells in the epidermal root, and nails from the nail matrix, both derived from epidermal keratinocytes. The dermis supports follicles with connective tissue and vessels but doesn't grow them. The hypodermis (subcutaneous tissue) provides fat and anchoring, not growth. The epidermis's role in generating these keratinized appendages, through cell division in basal layers, makes it the correct layer, per integumentary development.

Correct Answer: C

Rationale: The integumentary system's primary function is protection, shielding the body from pathogens, UV radiation, and physical damage via the skin, hair, and nails. Nutrient storage occurs in the hypodermis, a secondary role. Sensation, via receptors, is important but not primary. Gas exchange is the respiratory system's job, not skin's. Protection, encompassing barriers like the stratum corneum and immune responses, defines the system's core purpose, making it the correct answer.

Correct Answer: B

Rationale: Arrector pili muscles contract to pull hair shafts upright, historically aiding insulation or threat display, though 'ejecting' is imprecise modern texts favor 'generating goosebumps.' Sweat production is glandular, heat generation isn't their role (vasculature handles that), and collagen comes from fibroblasts. Their action on hair shafts, causing piloerection, aligns with this option's intent, making it the closest match despite terminology debate.