Which stratum of the epidermis protects the body against water loss and abrasion?

Correct Answer: D

Rationale: The stratum corneum, the outermost epidermal layer, protects against water loss and abrasion with its dead, keratin-filled cells and lipid barriers. The stratum germinativum (basale) generates cells, not protection. The lucidum, in thick skin, is a transitional layer, not the main shield. The corneum's role as the skin's durable, waterproof surface, constantly abraded and renewed, makes it the critical protective stratum, per epidermal function.

Correct Answer: D

Rationale: Nails, hardened epidermal extensions, aid manipulation and gripping by providing a rigid surface for fingertips, enhancing dexterity and tool use. Temperature regulation involves sweat and vessels, not nails. Sensation occurs via skin receptors, not nails themselves. UV protection is melanin's role, not nails'. The nails' mechanical support, protecting fingertips and assisting in tasks like scratching or picking, makes manipulation their key function, a practical role in the integumentary system.

Correct Answer: D

Rationale: Thermoreceptors, specialized nerve endings in the dermis and epidermis, detect temperature changes, signaling heat or cold to maintain homeostasis. Meissner's corpuscles sense light touch, Ruffini endings detect stretch and sustained pressure, and Merkel cells (via discs) sense continuous touch, none primarily temperature-focused. Thermoreceptors' sensitivity to thermal stimuli, distinct from mechanical or tactile roles, makes them the correct receptor type, essential for skin's sensory function.

Correct Answer: C

Rationale: Excretion via skin involves sweat glands eliminating waste like salts, urea, and water, a minor but real function alongside thermoregulation. Thermoregulation cools via sweat evaporation, sensation detects stimuli, and protection shields from harm, but only excretion directly addresses waste removal. This process, though secondary to kidney function, occurs through eccrine glands, making it the correct function.

Correct Answer: A

Rationale: The epidermis is primarily keratinocytes, epithelial cells that produce keratin, forming its stratified layers from basale to corneum, comprising about 90% of its cells. Fibroblasts, in the dermis, make collagen. Adipocytes, fat cells, dominate the hypodermis. Chondrocytes form cartilage, not skin. Keratinocytes' prevalence and role in barrier formation define the epidermis, making them the correct cell type.