The subcutaneous tissue (hypodermis) primarily contains:

Correct Answer: B

Rationale: The subcutaneous tissue, or hypodermis, primarily contains adipose tissue, fat cells that insulate and store energy, cushioning underlying structures. Blood vessels and sweat glands are mostly in the dermis, though some vessels traverse the hypodermis. Collagen fibers dominate the dermis, not the hypodermis, which has looser connective tissue. Melanocytes are epidermal, not subcutaneous. Adipose tissue's prevalence defines the hypodermis's role, distinguishing it from skin layers above, making this the correct content.

Correct Answer: C

Rationale: Lubrication and protection involve sebum production by sebaceous glands, moisturizing skin and hair while adding a protective layer against microbes and dryness. Thermoregulation uses sweat, sensation involves receptors, and vitamin D synthesis uses UV, none tied to oil. Sebum's role in maintaining skin integrity and suppleness defines this function, making it the correct answer.

Correct Answer: D

Rationale: The hypodermis insulates via adipose tissue, reducing heat loss, and stores energy as fat reserves, supporting survival during scarcity. Sweat production and temperature regulation (via vessels) occur in the dermis. The physical barrier is the epidermis's role. Insulation and energy storage define the hypodermis's primary function, cushioning and sustaining the body, making this the correct answer.

Correct Answer: C

Rationale: The epidermis is primarily keratinocytes, stratified epithelial cells that produce keratin, forming its layers from basale to corneum, about 90% of its composition. Fibroblasts are dermal, melanocytes produce melanin (a minority), and sebocytes (in sebaceous glands) are dermal, not epidermal. Keratinocytes' dominance and barrier role define the epidermis, making them the correct cell type.