Which protein waterproofs the hair?

Correct Answer: C

Rationale: Hair's waterproofing property stems from keratin, a tough, fibrous protein produced by keratinocytes in the hair follicle. Keratin forms the hair shaft's structure, creating a hard, insoluble layer that repels water and protects against environmental damage. This protein's high sulfur content, from cysteine amino acids, forms disulfide bonds, enhancing its durability and water resistance. Collagen, a major protein in the dermis, provides strength and support to skin but does not waterproof hair, as it's not a component of the hair shaft. Elastin, also in the dermis, offers flexibility, not waterproofing, and is absent in hair. Carotene is a pigment contributing to skin and hair color, not a protein or waterproofing agent. Keratin's role extends beyond hair to the epidermis, where it similarly prevents water loss, but in hair, its dense packing in the cuticle layer ensures a hydrophobic surface. This adaptation is critical for mammals, protecting hair from moisture-related degradation, making keratin the clear answer.

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.

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.