It is false that the epidermis:

Correct Answer: A

Rationale: The epidermis, the outermost skin layer, has specific characteristics that define its role as a protective barrier. It is not highly vascular; it lacks blood vessels entirely, relying on diffusion from the dermis for nutrients. This avascular nature distinguishes it from the dermis, which is rich in blood supply. The epidermis does contain melanin, produced by melanocytes, and keratin, formed as cells mature, both essential for protection and strength. It is distinctly stratified, with layers like the stratum germinativum, spinosum, granulosum, and corneum reflecting its cellular progression. It also gives rise to sebaceous and sweat glands, which develop as epidermal invaginations into the dermis. The false statement is the claim of vascularity, as the epidermis's lack of blood vessels is a fundamental feature, ensuring it remains a tough, renewable barrier while depending on underlying tissues for sustenance, a design critical to its function.

Correct Answer: C

Rationale: The arrector pili are small muscles attached to hair follicles, controlled by the sympathetic nervous system. When stimulated (e.g., by cold or fear), they contract, pulling the hair upright and causing the skin to pucker, resulting in goose bumps (piloerection). They are not glands, so they don't secrete anything like sebum (which comes from sebaceous glands) or sweat (from sweat glands). Excessive sweating is linked to eccrine glands, not arrector pili. Their role in creating goose bumps is a well-known physiological response to sympathetic activation, conserved from animals raising fur for warmth or defense, making this the correct function.

Correct Answer: A

Rationale: The stratum corneum, the outermost epidermal layer, is composed of dead, keratinized cells that form a waterproof barrier, preventing water loss and keeping the body from drying out. The stratum basale generates new cells but doesn't block water loss. The stratum spinosum provides strength, not a moisture barrier. The stratum granulosum begins keratinization, but the corneum completes it, acting as the skin's primary shield against dehydration. This layer's lipid-rich, tough structure is why humans don't shrivel like the fish, making it the key protective layer.

Correct Answer: C

Rationale: Adipose tissue, a type of connective tissue rich in fat cells, is found in the hypodermis, the deepest layer of the integumentary system. The hypodermis, also called the subcutaneous layer, lies beneath the dermis and serves as an energy reserve, insulator, and cushion for underlying structures like muscles and bones. The dermis, above the hypodermis, contains dense connective tissue with collagen and elastic fibers, blood vessels, and glands, but not significant adipose tissue. The epidermis, the outermost layer, is composed of stratified squamous epithelium, a keratinized tissue focused on protection, not fat storage. 'Stratified Squamous' as an option likely refers to the epidermis's tissue type, not a distinct layer, and lacks adipose tissue. The hypodermis's fat content varies by body region and individual, but its role in lipid storage is consistent, distinguishing it from the dermis's structural support and the epidermis's barrier function. This anatomical arrangement ensures the skin's protective and metabolic roles are compartmentalized effectively.

Correct Answer: B

Rationale: Acne arises from multiple factors, but excess sebum is a primary cause. Sebaceous glands produce sebum, an oil that lubricates skin and hair. Overproduction, often triggered by hormonal changes (e.g., androgens in puberty), clogs hair follicles, creating a breeding ground for Propionibacterium acnes bacteria. This leads to inflammation, forming pimples. Hypersecretion of hormones, like testosterone, drives this excess sebum, making it a linked cause, though the question allows single selection, prioritizing sebum's direct role. Excess carotene affects skin color, not oil production or acne. Poor hygiene ('wash your face') can worsen acne by allowing bacterial buildup, but it's not the root cause overwashing may even irritate skin. Bacterial infection is a secondary factor after sebum clogs pores. Dermatological consensus highlights sebum's role in acne pathogenesis, with hormonal influence as a trigger, distinguishing it from dietary pigments or hygiene alone as the most immediate explanation.