Which layer of the skin is responsible for the growth of hair and nails?

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: 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.

Correct Answer: A

Rationale: Thermoregulation involves sweating (eccrine glands) and blood vessel dilation/constriction in the dermis to manage heat loss or retention, maintaining body temperature. Sensation detects stimuli, lubrication uses sebum, and vitamin D synthesis relies on UV, not temperature control. This dual mechanism of sweat evaporation and vascular adjustment defines thermoregulation, making it the correct function.

Correct Answer: A

Rationale: Eccrine sweat glands produce odorless sweat, mostly water, electrolytes, and waste (e.g., urea), for cooling and excretion, secreted directly to the skin surface. Apocrine glands produce thicker, odorous sweat into hair follicles. Sebaceous glands secrete sebum, not sweat. 'Merocrine' is a synonym for eccrine, but eccrine is the standard term. Their watery, non-odorous output defines their role, making this the correct type.