Which of the following is not a function of the integument?

Correct Answer: B

Rationale: The integumentary system, primarily the skin, performs several critical physiological roles. It prevents dehydration by acting as a barrier, thanks to the waterproof keratin in the epidermis, which limits water loss. It regulates body fluids indirectly through sweat production and prevents excessive fluid loss. Temperature regulation occurs via sweating and blood vessel dilation or constriction in the dermis. However, the skin does not synthesize vitamin A. Instead, it synthesizes vitamin D when exposed to ultraviolet light, using cholesterol precursors in the epidermis. Vitamin A, essential for skin health and vision, is obtained from the diet (e.g., through beta-carotene) and not produced by the integument. This distinction is key: while the skin processes certain vitamins, its synthetic capacity is limited to vitamin D, not A. Misattributing vitamin A synthesis to the skin overlooks its actual metabolic role and dietary dependency, making this the function it does not perform among the listed options.

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: 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: 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.