What is the protein that fills the outermost dead cells of the epidermis?

Correct Answer: D

Rationale: Keratin is the fibrous protein that fills the dead cells of the stratum corneum, the outermost epidermal layer, providing toughness and resistance to abrasion. Granstein and dermin are not recognized proteins in skin anatomy likely distractors. Melanin, produced by melanocytes deeper in the epidermis, is a pigment for UV protection, not a structural filler in dead cells. Keratin, produced by keratinocytes as they move upward and die, hardens the corneum, forming a protective barrier, a process well-documented in histology as essential to skin's durability and waterproofing.

Correct Answer: A

Rationale: The integumentary system officially includes the epidermis and dermis. The epidermis is the outer protective layer, while the dermis beneath it contains connective tissue, glands, and nerves. The hypodermis, though adjacent, is the subcutaneous layer, not part of the integument proper. Listing epidermal sublayers (germinativum to corneum) excludes the dermis, incomplete for the integument. Combining the corneum with dermal layers omits other epidermal parts. Standard anatomy defines the integument as epidermis and dermis, aligning with their integrated protective roles.

Correct Answer: A

Rationale: Sebaceous glands are the skin's oil glands, secreting sebum into hair follicles to lubricate skin and hair, distinct from sweat glands. Eccrine (merocrine) glands secrete watery sweat to the surface. Apocrine glands secrete sweat into follicles. The term 'sebaceous' directly refers to oil production, a role not shared by the others, all of which are sudiferous glands. This specificity in skin histology identifies sebaceous glands as the oil producers, making them the correct synonym.

Correct Answer: C

Rationale: The hypodermis, or superficial fascia, is the subcutaneous layer of fat and connective tissue beneath the dermis, not part of the integument (epidermis and dermis). It's not the outer layer (epidermis) or inner layer of the skin proper (dermis is deeper within the integument). It is vascularized, with blood vessels supplying it, not reliant solely on diffusion like the epidermis. Its exclusion from the integument and role as a cushion and insulator define it anatomically, making this the correct characterization.

Correct Answer: B

Rationale: Keratinocytes, originating in the stratum basale, migrate upward, producing keratin and dying to form the stratum corneum, the dead, keratin-filled outer layer. Melanocytes produce melanin, not the corneum's structure. Dendrocytes (dendritic cells) are immune-related, not structural. Lymphocytes are in blood or lymph, not forming skin layers. Keratinocytes' differentiation into the corneum's protective barrier is a core epidermal process, making them the responsible cell type.