Choose the incorrect statement below.

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: 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.

Correct Answer: D

Rationale: Full-thickness burns over 20% destroy the epidermis and dermis, removing the waterproof stratum corneum, causing rapid water loss leading to dehydration and shock a primary life threat. Thermoregulation is impaired but secondary to fluid loss. Vitamin D loss isn't immediately fatal. Urea and uric acid excretion is minimal via skin (mostly kidneys), not a key issue. Water loss, a critical consequence of losing the skin barrier, is the dominant factor, as evidenced by burn treatment prioritizing fluid replacement.

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.