Which tissue region do nails originate from?

Correct Answer: C

Rationale: Nails originate from the nail matrix, a specialized epidermal region beneath the proximal nail fold. The matrix contains actively dividing keratinocytes that produce the nail plate, a hard keratin structure, through keratinization. As cells proliferate, they push the nail forward over the nail bed, determining its growth and thickness. The eponychium, or cuticle, is the skin fold overlapping the nail's base, protecting the matrix but not forming the nail. The lunula, the white crescent at the nail's base, is part of the matrix visible through the thin nail, not the origin. 'Cuticle' often refers to the eponychium in common use, but anatomically, it's not the nail's source. The matrix's role is evident in nail regrowth after injury damage here alters nail shape, unlike other regions. Dermatological texts confirm the matrix as the nail's generative tissue, distinguishing it from surrounding protective or visible parts.

Correct Answer: D

Rationale: Keratinocytes produce keratin, forming the skin's tough outer layer correct. Merkel cells connect to sensory nerve endings for touch correct. Melanocytes produce melanin for pigmentation correct. Dendrocytes (likely meaning dendritic cells or macrophages in the dermis) don't produce 'dendrocidin,' a non-existent substance, making this incorrect. Dendritic cells process antigens for immunity, not a specific secretion like dendrocidin. The error lies in this fabricated term, inconsistent with skin cell functions, identifying it as the false statement.

Correct Answer: B

Rationale: The stratum corneum is the most superficial skin layer, forming the horny, keratinized surface of the epidermis that protects against abrasion and water loss. The stratum lucidum, found in thick skin, lies just beneath it. The papillary and reticular dermal layers are in the dermis, below the epidermis, with the papillary being more superficial but still deeper than the corneum. As the outermost barrier, constantly shedding and renewing, the stratum corneum holds the top position in skin structure, making it the clear choice.

Correct Answer: B

Rationale: Vitamin D, as calcitriol, is crucial for calcium absorption in the gut, enhancing intestinal uptake to maintain blood calcium levels for bone health and muscle function. Haemostasis (clotting) relies on calcium but not directly on vitamin D production. Erythropoiesis (red blood cell formation) needs other factors like erythropoietin, not vitamin D. Intrinsic factor aids vitamin B12 absorption, unrelated to vitamin D. The skin-initiated, liver- and kidney-activated vitamin D process targets calcium regulation, a primary physiological role, making this the correct purpose.

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.