An individual using a sharp knife notices a small amount of blood where he just cut himself. Which of the following layers of skin did he have to cut into in order to bleed?

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: 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.

Correct Answer: C

Rationale: Nails originate from the nail matrix, a specialized epidermal region beneath the proximal nail fold. The matrix contains actively dividing keratinocytes that produce the nail plate, a hard keratin structure, through keratinization. As cells proliferate, they push the nail forward over the nail bed, determining its growth and thickness. The eponychium, or cuticle, is the skin fold overlapping the nail's base, protecting the matrix but not forming the nail. The lunula, the white crescent at the nail's base, is part of the matrix visible through the thin nail, not the origin. 'Cuticle' often refers to the eponychium in common use, but anatomically, it's not the nail's source. The matrix's role is evident in nail regrowth after injury damage here alters nail shape, unlike other regions. Dermatological texts confirm the matrix as the nail's generative tissue, distinguishing it from surrounding protective or visible parts.

Correct Answer: C

Rationale: Full-thickness burns, which destroy both the epidermis and dermis, eliminate the skin's waterproof barrier, primarily the stratum corneum, leading to uncontrolled water loss from exposed tissues. This can cause severe dehydration and hypovolemic shock, making it life-threatening when over 20% of the body surface is affected. While vitamin D synthesis occurs in the skin, its loss isn't immediately fatal. Loss of sensation is a concern but not the primary threat. Abrasion of internal tissues happens but is secondary to fluid loss and infection risk (not listed but noted in the source). The critical issue is the skin's inability to retain water, a fundamental protective function, making this the key reason for the severity.

Correct Answer: D

Rationale: Keratinocytes produce keratin, forming the skin's tough outer layer correct. Merkel cells connect to sensory nerve endings for touch correct. Melanocytes produce melanin for pigmentation correct. Dendrocytes (likely meaning dendritic cells or macrophages in the dermis) don't produce 'dendrocidin,' a non-existent substance, making this incorrect. Dendritic cells process antigens for immunity, not a specific secretion like dendrocidin. The error lies in this fabricated term, inconsistent with skin cell functions, identifying it as the false statement.