Which statement about vitamin D is INCORRECT?

Correct Answer: C

Rationale: Vitamin D aids calcium uptake, is synthesized starting in the skin (UV converts 7-dehydrocholesterol), modified in the liver, and activated in the kidneys correct. It's a steroid hormone when active (calcitriol), also correct. However, it's not essential in the diet because the body can produce it via sunlight, making this statement incorrect. Dietary intake supplements natural production, but it's not required if UV exposure is adequate, a distinction in nutritional science that identifies this as the false claim.

Correct Answer: B

Rationale: Keratin, produced by keratinocytes, is the most common epidermal protein, filling the stratum corneum and providing strength and protection. Elastin is in the dermis for elasticity, not the epidermis. Melanin is a pigment, less abundant than keratin structurally. Cholesterol exists in cell membranes but isn't a dominant protein. Keratin's prevalence, forming the epidermis's tough outer layers, is a hallmark of skin histology, making it the correct answer.

Correct Answer: B

Rationale: The stratum corneum consists of dead, keratinized cells, forming a protective barrier shed through abrasion correct. Cell division occurs in the stratum basale, not corneum. Collagen, elastin, and reticular fibers are dermal, not in the avascular corneum. Sensory receptors reside in the dermis or deeper epidermis, not the dead corneum. Its dead cell composition is its defining trait, making this the accurate statement.

Correct Answer: C

Rationale: The hypodermis, also called subcutaneous tissue, contains adipose tissue that insulates the body against heat loss and stores energy as fat reserves. The epidermis is a thin, avascular layer of epithelial cells, lacking fat. The dermis has connective tissue, glands, and vessels, but not significant adipose. 'Subcutaneous tissue' is synonymous with hypodermis, reinforcing its role. The hypodermis's fat content, cushioning organs and providing a calorie reserve, distinguishes it from the skin's upper layers, making it the correct answer.

Correct Answer: B

Rationale: Pacinian corpuscles, deep pressure and vibration sensors, are located in the dermis, often near its border with the hypodermis, within the reticular layer. The epidermis, avascular and superficial, lacks such receptors. The hypodermis (subcutaneous tissue) may contain some, but they're primarily dermal, integrated with nerve networks there. The dermis's role as the sensory and structural layer, housing various receptors, makes it the correct location for these lamellated corpuscles.