The most probable cause of alopecia is:

Correct Answer: C

Rationale: Alopecia, or hair loss, has multiple potential causes, but one predominates. Protein deficiencies can weaken hair, as keratin requires amino acids, but this is rare in well-nourished populations and not the leading cause. Dermal viral infections might cause localized hair loss (e.g., fungal infections like ringworm), but they are not primary alopecia triggers. Stress can induce temporary hair loss (telogen effluvium), where hair follicles enter a resting phase, but it's reversible and less common as a chronic cause. Genetic inheritance, particularly androgenetic alopecia (male or female pattern baldness), is the most probable and widespread cause, affecting millions globally. Driven by hormones (androgens) and genetics, it leads to progressive follicle miniaturization. Studies show its prevalence up to 50% of men and 25% of women by age 50 outstrips other causes. Its permanence and familial patterns distinguish it as the dominant etiology, aligning with clinical observations and epidemiological data.

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.

Correct Answer: B

Rationale: Skin fibers, primarily collagen in the dermis, are arranged in bundles called lines of cleavage (or Langer's lines). These parallel alignments reflect the natural tension and orientation of collagen and elastic fibers in the reticular dermis, giving skin strength and flexibility. Surgeons use these lines for incisions, as cuts along them heal with less scarring due to minimal fiber disruption. The zone of hyperaemia is a region of increased blood flow, not a fiber structure. Epidermal ridges, on the epidermis, form fingerprints from dermal papillae, not fiber bundles. The stratum lucidum, an epidermal layer in thick skin, consists of dead cells, not fibers. Lines of cleavage are a dermal feature, visible in histological sections as organized collagen, critical for skin's mechanical properties and surgical outcomes, distinguishing them from epidermal or vascular terms.