Which of the following is a disease characterized by the presence of hives?

Correct Answer: D

Rationale: Urticaria, commonly known as hives, is a skin condition characterized by raised, itchy welts due to allergic or other triggers. Keloids are overgrown scars, not hives. Seborrhea involves oily, scaly skin, unrelated to hives. Eczema causes itchy, inflamed skin but typically as patches, not distinct welts like hives. Urticaria specifically matches the definition of hives, with its hallmark transient, raised lesions, making it the correct disease.

Correct Answer: A

Rationale: The epidermis is a dynamic tissue where cells are continuously renewed. The stratum germinativum, the deepest layer, generates new cells via mitosis. These cells migrate upward, differentiating through the spinosum, granulosum, and, in thick skin, lucidum layers, before reaching the stratum corneum as dead, keratinized cells. This process, known as epidermal turnover, takes approximately 15-20 days in healthy adults, though it can vary slightly (e.g., 10-30 days) depending on age, health, and location. A 6-8 week or 12-15 week timeline is far too long for this cellular journey, as it would imply a sluggish renewal rate inconsistent with the skin's protective role. An 8-10 day estimate is too short for full differentiation and migration. The 15-20 day range reflects the balance between cell production and shedding, supported by dermatological studies, ensuring the skin maintains its barrier function efficiently.

Correct Answer: A

Rationale: Langerhans cells are immune cells (dendritic cells) primarily located in the stratum spinosum of the epidermis, where they play a key role in detecting pathogens and initiating immune responses. The stratum spinosum, with its multiple layers of spiky keratinocytes, provides an ideal environment for these cells to patrol for invaders. The stratum corneum, being composed of dead, keratinized cells, lacks living cells like Langerhans. The stratum granulosum is a thin layer focused on keratin production, not immune function, and the stratum basale, while active in cell division, hosts fewer Langerhans cells compared to the spinosum. Research on skin histology confirms that Langerhans cells are most abundant in the stratum spinosum, aligning with their role in immune surveillance.

Correct Answer: B

Rationale: The nail growth center is the nail matrix, located beneath the nail root at the proximal end of the nail. The hyponychium is the skin under the free edge of the nail, at the distal end, making it the furthest from the matrix. The nail bed lies directly beneath the nail plate, extending from the root to the free edge, but not as far as the hyponychium. The nail root is the proximal part where growth originates, and the eponychium is the skin fold over the root. Since the hyponychium is at the nail's distal tip, opposite the growth center, it's the furthest structure.

Correct Answer: D

Rationale: Severe sunburn with pain and blisters indicates damage beyond the epidermis into the dermis. The epidermis, especially the stratum basale, gets UV damage first, causing redness and pain, but blisters form when fluid accumulates between the epidermis and dermis due to deeper injury, affecting dermal blood vessels and nerves. The hypodermis, a fatty layer, isn't typically involved in sunburn unless damage is extreme. Epidermis-only damage wouldn't produce blisters, and hypodermis-only is implausible. The epidermis and dermis combination matches the symptoms of a second-degree burn from sun exposure.