Which of the following is not a physiological possibility of the integument?

Correct Answer: D

Rationale: The integument performs diverse physiological roles. It eliminates salts, urea, and uric acid through sweat, a minor excretory function alongside the kidneys. It absorbs fat-soluble vitamins (e.g., A, D, E, K), steroids, and toxins through its lipid-rich layers, as seen in transdermal drug delivery. The hypodermis stores lipids as adipose tissue, providing energy and insulation. However, the skin does not synthesize proteins and carbohydrates. It produces keratin (a protein) and vitamin D (a sterol), but this involves assembly from dietary precursors, not de novo carbohydrate or protein synthesis, which occurs in the liver or muscles. Keratin forms via epidermal differentiation, not true synthesis, and carbohydrates are not made in skin cells. This limitation reflects the integument's specialized roles protection, sensation, and minor excretion versus metabolic organs' broader synthetic capacities, making this the impossible function among the options.

Correct Answer: C

Rationale: Skin cancers, like melanoma and squamous cell carcinoma, are strongly linked to UV exposure from the sun, and limiting this exposure (via sunscreen, clothing, or shade) reduces risk significantly. They're not always easily treatable melanoma can be deadly if it metastasizes. Poor hygiene doesn't cause skin cancer; it's unrelated to UV-induced DNA damage. They don't affect only the epidermis; advanced cases invade the dermis and beyond. Public health data supports sun protection as a proven preventive measure, making this the most accurate statement.

Correct Answer: B

Rationale: Tattoo ink is injected into the dermis, the thick layer beneath the epidermis. The epidermis, the outermost layer, constantly renews itself, shedding dead cells from the stratum corneum every few weeks. If ink were placed here, it would fade quickly as cells slough off. The dermis, however, is stable, containing collagen, blood vessels, and nerves, and does not regenerate rapidly. Tattoo needles penetrate about 1-2 mm deep, depositing ink into this layer, where it remains trapped by fibroblasts and immune cells, ensuring permanence. The hypodermis (or subcutaneous layer, also listed as 'SubQ') lies deeper, storing fat, and is too far below the surface for tattoo visibility or precision. Injecting ink there would blur the design and miss the dermis's ideal depth. The dermis's vascularity can cause initial bleeding, but its stationary nature preserves the tattoo long-term, a fact exploited by tattoo artists globally, confirming it as the target layer.

Correct Answer: B

Rationale: The nail's anatomy includes specific structures, but 'nail head' is not among them. The nail body (or plate) is the hard, visible keratinized portion covering the nail bed. The nail matrix, beneath the proximal nail fold, is the growth zone where new cells form, pushing the nail forward. The eponychium, or cuticle, is the skin fold at the nail's base, protecting the matrix. These are standard nail components, derived from epidermal keratinization. 'Nail head' is not a recognized anatomical term in human nail structure possibly a confusion with other contexts (e.g., a tool) or a misnomer. In contrast, terms like lunula (the white crescent) or hyponychium (skin beneath the nail's free edge) are valid but not listed. The absence of 'nail head' in anatomical texts and its irrelevance to nail growth or function distinguish it as the incorrect option, aligning with standard dermatological descriptions.

Correct Answer: B

Rationale: Lipid-soluble molecules pass most easily through the epidermis due to its structure. The stratum corneum, rich in keratin and lipids (e.g., ceramides, cholesterol), forms a hydrophobic barrier. Lipid-soluble substances, like steroids or fat-soluble vitamins (A, D, E, K), dissolve into this lipid matrix, diffusing through cell membranes and intercellular spaces. Proteins, large and often hydrophilic, cannot penetrate this barrier, remaining excluded unless via wounds. Water-soluble compounds, like glucose, struggle to cross without carriers, as the corneum repels water. Salts, ionic and water-soluble, face similar resistance, though sweat ducts allow minimal passage. Transdermal drug delivery exploits this, using lipid-based patches for absorption. The epidermis's avascularity and lipid composition favor nonpolar molecules, a principle backed by pharmacological and physiological research, distinguishing lipid-soluble penetration from polar or large substances.