Which of the following is not a type of integumentary sensory receptor?

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: 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.

Correct Answer: B

Rationale: Among skin cancers, malignant melanoma is the most deadly due to its aggressive nature and high metastatic potential. Originating in melanocytes, the pigment-producing cells in the epidermis, it can spread rapidly to lymph nodes, lungs, and brain if untreated, with a 5-year survival rate dropping significantly in advanced stages (e.g., below 30% for stage IV). Basal cell carcinoma, the most common skin cancer, arises from basal cells in the epidermis and rarely metastasizes, making it highly treatable with surgery. Squamous cell carcinoma, from squamous cells, can metastasize but does so less frequently and aggressively than melanoma, with better prognosis if caught early. Melanoma's lethality stems from its ability to invade deeper tissues and its link to UV exposure, which triggers mutations (e.g., in the BRAF gene). Statistics show it causes the majority of skin cancer deaths despite being less common, emphasizing its severity over the slower-growing, less invasive basal and squamous types.

Correct Answer: B

Rationale: Sebaceous glands, found in the dermis near hair follicles, produce sebum, an oily substance. Sebum, a mix of lipids like triglycerides and wax esters, lubricates hair and skin, preventing dryness and offering minor antimicrobial protection. It's secreted via a holocrine process cells disintegrate to release it into follicles, then to the skin surface. Milk is produced by mammary glands, modified sweat glands, not sebaceous ones. Sweat comes from eccrine and apocrine glands, distinct from sebaceous function, with water and salts, not oil. Cerumen (earwax) is made by ceruminous glands in the ear canal, a specialized sebaceous type, but not typical skin sebaceous glands. Sebum's oily nature distinguishes it, supporting skin flexibility and waterproofing, a role confirmed by histological and physiological studies of gland activity, setting it apart from other secretions.