It is false that the dermis:

Correct Answer: B

Rationale: The dermis, a thick layer beneath the epidermis, is a complex structure with multiple components and functions. It is highly vascular, with blood vessels supplying nutrients and aiding in thermoregulation. It contains reticular and elastic fibers for strength and flexibility, as well as smooth muscle (e.g., arrector pili muscles) and numerous nerve endings for sensation. However, it does not give rise to sebaceous and sweat glands. These glands originate from the epidermis during embryonic development, invaginating downward into the dermis as they mature. Sebaceous glands secrete oil, and sweat glands produce sweat, both budding from epidermal tissue, not dermal. This embryological distinction is critical: while the dermis hosts these glands and supports them with blood and nerve supply, their cellular origin is epidermal. The statement is false because it misattributes the developmental source of these glands, contradicting histological and developmental biology principles.

Correct Answer: C

Rationale: The hypodermis, or subcutaneous layer, is a fatty layer beneath the dermis that protects underlying organs by cushioning them, helps maintain body temperature through insulation, and serves as a long-term energy storage site via adipose tissue. However, it is not a source of blood vessels in the epidermis. The epidermis itself is avascular (lacking blood vessels), relying on diffusion from the papillary dermis, not the hypodermis, for nutrients. The hypodermis does contain larger blood vessels, but they supply the dermis, not directly the epidermis. This distinction in vascular anatomy excludes the hypodermis as a direct source for epidermal blood vessels, making it the correct choice for what is not a function.

Correct Answer: C

Rationale: Bleeding occurs when blood vessels are damaged, and the epidermis (stratum corneum, granulosum, bas fragility ale) is avascular, containing no blood vessels. The papillary dermis, the upper dermal layer, has a rich supply of capillaries that can bleed if cut. The stratum corneum is dead and superficial, the stratum granulosum is a thin transitional layer, and the stratum basale, while alive, relies on diffusion from dermal vessels, not having its own. A cut reaching the papillary dermis, just below the epidermis, would nick these capillaries, causing minor bleeding, making it the correct layer.

Correct Answer: C

Rationale: The skin plays a unique role in vitamin production, specifically synthesizing vitamin D when exposed to ultraviolet (UV) light from the sun. This process occurs in the epidermis, where UV rays convert 7-dehydrocholesterol into previtamin D3, which then becomes vitamin D3 (cholecalciferol). This vitamin is crucial for calcium absorption and bone health. Vitamin A, essential for skin cell development, is not synthesized by the skin but obtained through diet (e.g., from beta-carotene). Vitamin C, an antioxidant vital for collagen synthesis, is also diet-derived, not produced in the skin. Vitamin E, another antioxidant protecting skin cells, is similarly acquired through food or supplements, not manufactured by the integument. The skin's ability to produce vitamin D distinguishes it from other vitamins, an evolutionary adaptation to ensure adequate levels in sunlight-exposed populations. This synthesis is regulated by exposure time and skin pigmentation, with darker skin requiring more UV exposure due to melanin's filtering effect. Thus, vitamin D is the only vitamin the skin synthesizes, aligning with its physiological role.

Correct Answer: B

Rationale: Skin color results from three key contributors: carotene, melanin, and hemoglobin. Melanin, produced by melanocytes in the epidermis, provides brown to black tones, varying by amount and type (eumelanin vs. pheomelanin), and protects against UV damage. Carotene, a dietary pigment, accumulates in the stratum corneum and hypodermis, adding yellowish hues, noticeable in lighter skin or excess intake. Hemoglobin, in dermal blood vessels, imparts pink or red tones based on oxygenation oxygenated blood brightens skin, while deoxygenated blood (cyanosis) dulls it. Keratin, a structural protein in the epidermis and hair, is colorless and waterproofs but doesn't pigment skin. Combining melanin's depth, carotene's tint, and hemoglobin's flush explains the full spectrum of human skin tones, from pale to dark, across populations. Omitting any of these misrepresents the complex interplay, with melanin dominant in darker skin and hemoglobin's effect more visible in lighter complexions, making this trio the accurate basis.