Which of the following is a disease characterized by a skin rash that is blistering and itchy?

Correct Answer: C

Rationale: Eczema, particularly atopic dermatitis, is a chronic condition causing an itchy, blistering rash, often with small fluid-filled vesicles that can weep or crust. Keloids are firm scars, not rashes. Seborrhea produces oily scales, not blisters. Urticaria causes itchy welts, but they're typically not blistering. Eczema fits the description of a rash that is both blistering (in acute phases) and intensely itchy, aligning with its clinical presentation, making it the correct choice.

Correct Answer: D

Rationale: The skin contains various sensory receptors that detect stimuli like pressure, touch, temperature, and pain. Pacinian corpuscles are deep in the dermis and hypodermis, sensing deep pressure and vibration. Free nerve endings, widespread in the epidermis and dermis, detect pain, temperature, and light touch. Ruffini corpuscles, also in the dermis, respond to skin stretch and sustained pressure. Krause corpuscles (listed elsewhere in the document) sense cold. All listed options Pacinian corpuscles, free nerve endings, and Ruffini corpuscles are indeed integumentary sensory receptors, each with specialized roles in mechanoreception or nociception. 'None of the above' implies that all are receptors, which is correct here, as no non-receptor is listed. The skin's sensory array supports its role as a sensory organ, and excluding any of these would misrepresent its capabilities. Thus, the option indicating all are receptors aligns with their documented presence and function in the integument.

Correct Answer: C

Rationale: The dermis consists of two layers: the papillary (upper) and reticular (lower), both primarily made of connective tissue, including collagen and elastin fibers, which provide strength, elasticity, and support. The papillary layer has loose connective tissue with blood vessels and nerves, while the reticular layer is denser with thick collagen bundles. Melanocytes, which produce pigment, are found in the epidermis, not the dermis. Keratinocytes, the main epidermal cells, form the skin's outer layers, not the dermis. Adipose tissue is characteristic of the hypodermis, beneath the dermis, not within it. The connective tissue composition of the dermis is fundamental to its structural and protective roles, making it the correct answer.

Correct Answer: A

Rationale: Skin exposure to sunlight, specifically UVB rays, triggers vitamin D synthesis by converting 7-dehydrocholesterol in the epidermis to vitamin D3 (cholecalciferol), essential for calcium absorption and bone health. Arteriole constriction occurs in response to cold, not sunlight, to reduce heat loss. Folate production isn't directly tied to sunlight; in fact, UV light can degrade folate in the skin. Thermoregulation involves sweating and blood flow adjustments, not a sunlight requirement. Vitamin D synthesis is a well-established photochemical process in the skin, making it the correct sunlight-dependent function.

Correct Answer: B

Rationale: Wound healing follows clotting (hemostasis) with inflammation, then proliferation, where fibroblasts in the dermis increase production of connective tissue (collagen) to rebuild the wound bed and form granulation tissue. Melanin production by melanocytes affects pigmentation, not repair. Pacinian corpuscles sense pressure, not part of healing, and their number doesn't increase. The stratum lucidum, a thin layer in thick skin, doesn't 'activate' in healing. Connective tissue production is the next key step in the proliferative phase, laying the foundation for wound closure, making it the correct response.