What purpose is vitamin D (calcitriol) used for?

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: 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.

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.