Sebaceous glands secrete

Correct Answer: A

Rationale: Sebaceous glands produce sebum, an oily substance that lubricates skin and hair, preventing dryness and aiding waterproofing. Impetigo is a bacterial infection, not a secretion. Serous refers to a watery fluid from serous glands, not sebaceous ones. 'Sirius' seems to be a typo or distractor (possibly meant 'serous'), but it's not relevant. Sebum is the specific secretion of sebaceous glands, tied to their role in skin health, making it the correct answer.

Correct Answer: A

Rationale: Melanin, produced by melanocytes in the stratum germinativum, is a pigment critical to skin function. Its primary role is to absorb and dissipate ultraviolet (UV) light, shielding underlying cells from DNA damage that can lead to mutations or skin cancer. Darker skin, with more melanin, offers greater UV protection, an adaptation seen in populations near the equator. Melanin does not prevent infections, a role more aligned with the skin's physical barrier and immune cells. It has a minor, indirect effect on temperature regulation by absorbing heat, but this is not its main purpose sweat glands and blood vessels handle that. Water loss is restricted by keratin, not melanin. Evolutionarily, melanin's UV-protective function is paramount, reducing sunburn and cancer risk, and its distribution in the epidermis optimizes this role, making protection from ultraviolet light its defining contribution to skin physiology.

Correct Answer: B

Rationale: Collagen is a protein abundant in the dermis, particularly the reticular layer, where it forms a network of fibers that give the skin its structure and tensile strength. This structural support helps skin resist stretching and tearing, maintaining its shape and integrity. Elasticity is primarily provided by elastin, another dermal protein, not collagen. Color comes from melanin, produced by melanocytes in the epidermis, not collagen. UV protection is also a function of melanin, not collagen, which has no pigment or light-absorbing properties. Collagen's role as the skin's scaffolding is well-documented in dermatology, making structure the most accurate description of its contribution.

Correct Answer: C

Rationale: The integumentary system protects via physical barriers and cellular structures. The stratum lucidum, a clear layer in thick skin, adds a tough barrier. Desmosomes anchor epidermal cells together, enhancing structural integrity against trauma. Merkel cells sense touch, indirectly aiding protection by detecting threats. Folic acid (folate) synthesis, however, isn't a skin function; folate is obtained from diet, and UV light actually breaks it down in skin, not contributing to protection. This metabolic process is unrelated to the integumentary system's protective role, making it the odd one out.

Correct Answer: C

Rationale: Squamous cell carcinoma (SCC) originates from keratinocytes, the predominant cells of the epidermis, specifically in the stratum spinosum, where they begin to differentiate. Basal cell carcinoma affects basal cells of the stratum basale, not SCC. Melanocytes in the basale produce melanin, linked to melanoma, not SCC. Langerhans cells are immune cells, not cancerous in SCC, and the stratum lucidum lacks them. SCC arises from spinosum keratinocytes due to UV-induced DNA damage, enabling it to invade deeper layers and metastasize if untreated, making this the correct cell type.