Full thickness burns to more than 20% of the skin surface is a life-threatening situation. Why is this?

Correct Answer: C

Rationale: Full-thickness burns, which destroy both the epidermis and dermis, eliminate the skin's waterproof barrier, primarily the stratum corneum, leading to uncontrolled water loss from exposed tissues. This can cause severe dehydration and hypovolemic shock, making it life-threatening when over 20% of the body surface is affected. While vitamin D synthesis occurs in the skin, its loss isn't immediately fatal. Loss of sensation is a concern but not the primary threat. Abrasion of internal tissues happens but is secondary to fluid loss and infection risk (not listed but noted in the source). The critical issue is the skin's inability to retain water, a fundamental protective function, making this the key reason for the severity.

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.

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.