If you cut yourself and bacteria enter the wound, which of the following cells would help get rid of the bacteria?

Correct Answer: C

Rationale: Langerhans cells, found mainly in the stratum spinosum, are dendritic immune cells that detect and engulf bacteria, presenting antigens to trigger an immune response. Merkel cells sense touch, not infection. Keratinocytes form the skin barrier and produce keratin, but they don't directly fight bacteria. Melanocytes produce melanin for pigment, not immunity. When bacteria breach a wound, Langerhans cells act as the epidermis's first line of immune defense, migrating to lymph nodes to alert the immune system, making them the critical cells in this scenario.

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: B

Rationale: The waterproof coating in epidermal cells is keratin, a fibrous protein forming the stratum corneum, the epidermis's outermost layer. Produced during keratinization, keratin fills dead keratinocytes, creating a tough, insoluble barrier that prevents water loss and entry. This hydrophobicity, due to keratin's sulfur-rich structure and tight packing, protects against dehydration and environmental damage, a key adaptation for terrestrial life. Myelin, a lipid sheath, insulates nerves, not skin cells. Melanin, a pigment from melanocytes, absorbs UV light but doesn't waterproof. Albumin, a blood protein, maintains osmotic pressure, unrelated to epidermal coating. Keratin's dominance in the corneum up to 85% of its dry weight ensures the skin's impermeability, a fact confirmed by studies of skin barrier function, setting it apart from pigments or unrelated proteins.

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.