The Epidermis forms from the germ layer, while the Dermis forms from the germ layer.

Correct Answer: A

Rationale: During embryonic development, the integumentary system's layers arise from distinct germ layers. The epidermis, the outer skin layer, forms from the ectoderm, the outermost embryonic layer responsible for external structures like skin, hair, and nails. Ectodermal cells differentiate into stratified squamous epithelium, eventually keratinizing for protection. The dermis, beneath the epidermis, develops from the mesoderm, the middle germ layer that generates connective tissues, muscles, and blood vessels. Mesodermal cells form the dermis's collagen, elastic fibers, and vascular network, supporting the epidermis. The endoderm, forming internal linings like the gut, contributes neither to the epidermis nor dermis. Reversing the layers (mesoderm for epidermis, ectoderm for dermis) contradicts embryology, as does involving endoderm. This ectoderm-mesoderm pairing reflects their specialized roles ectoderm for barrier formation, mesoderm for structural support consistent with developmental biology and the integument's dual-layer functionality.

Correct Answer: D

Rationale: Hypodermic administration means delivering a drug 'below the dermis' (from Greek 'hypo' meaning under), typically via injection into the subcutaneous fat layer (hypodermis) beneath the skin, as with insulin shots. Wiping onto the skin is topical, not hypodermic. A patch is transdermal, penetrating through the skin to the bloodstream. Injection into the dermis is intradermal, a shallower method used for tests like TB screening. Hypodermic injections target the fatty subcutaneous layer for slower absorption into circulation, a common medical practice, making this the precise definition.

Correct Answer: B

Rationale: Full-thickness skin burns destroy the epidermis and dermis, removing the waterproof stratum corneum and exposing underlying tissues, leading to rapid fluid loss (dehydration) and vulnerability to infection without the skin barrier. Stomach ulcers cause internal bleeding, not external fluid loss or skin infection risk. Muscle tears and bone fractures may bleed or infect, but they don't typically cause massive fluid loss like burns, as the skin remains intact. Burns' dual threat of fluid loss and pathogen entry, especially over large areas, makes them uniquely life-threatening, as seen in burn unit protocols.

Correct Answer: B

Rationale: Transdermal drugs, applied via patches, must penetrate the skin's lipid-rich stratum corneum, requiring lipid solubility to pass between keratinized cells and reach the bloodstream. Water-soluble drugs struggle to cross this waterproof barrier. Subcutaneous injection bypasses the skin, not transdermal. Chemo-receptor irritation is unrelated to transdermal delivery, which focuses on absorption, not sensory response. Lipid solubility, often enhanced by chemical formulation, is a pharmacological necessity for transdermal success, as seen in drugs like nicotine patches, making this the key requirement.

Correct Answer: A

Rationale: Vitamin D production starts in the skin when UVB radiation converts 7-dehydrocholesterol in the epidermis to previtamin D3, initiating the process. PTH signals the kidneys to activate vitamin D later, not the skin. Calcium presence is an outcome, not a trigger. Hydroxylation occurs in the liver and kidneys, not the skin, modifying the skin's product. UV exposure is the essential first step, a photochemical reaction unique to epidermal cells, making this the correct initiating condition.