Eccrine sweat glands

Correct Answer: B

Rationale: Eccrine sweat glands are distributed across the body's skin surface and produce a watery sweat composed of water, salts, and urea, primarily for thermoregulation by cooling the body through evaporation. They are not associated with hair (unlike apocrine glands), ruling out that option. Sebum is an oily secretion from sebaceous glands, not eccrine glands. While sweat hydrates the skin slightly, 'acting as a moisturizer' isn't their primary function, which is temperature control. Their widespread presence and watery output distinguish eccrine glands as key players in sweating, aligning perfectly with this description.

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.

Correct Answer: B

Rationale: Sensory receptors in the skin detect stimuli like touch, pressure, or pain. Meissner corpuscles sense light touch, root hair plexuses detect hair movement, and nociceptors register pain all are receptors in the dermis or epidermis. Apocrine glands, however, are sweat glands associated with hair follicles, secreting sweat in response to stress or hormones, not sensing stimuli. They're part of the skin's excretory system, not its sensory network. This functional distinction excludes apocrine glands from being sensory receptors, aligning with their role in secretion rather than perception.