The integumentary system consists of the skin and its appendages, including hair, nails, sweat glands, and sebaceous glands.

The skin is the largest organ by surface area and weight, providing protection and regulation.

The epidermis is the most superficial layer and provides a protective barrier.

Explanation:
The epidermis is made of stratified squamous epithelium, ideal for protection against abrasion.

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Melanin protects against ultraviolet radiation and determines skin color.

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Sweat evaporation helps regulate body temperature.

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Sebum lubricates and waterproofs the skin and hair.

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Hair follicles originate in the dermis.

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Keratin is a tough protein forming nails and hair.

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The dermis contains blood vessels, nerves, and connective tissue.

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The hypodermis stores fat for insulation and cushioning.

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Collagen and elastin fibers in the dermis provide tensile strength and elasticity.

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Eccrine glands regulate body temperature through sweat evaporation

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Apocrine glands become functional after puberty and respond to hormonal changes

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Dermal papillae form epidermal ridges, creating fingerprints.

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Ultraviolet light triggers vitamin D production in the skin.

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Dermatitis means inflammation of the skin.

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Blisters contain clear fluid between skin layers.

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Acne results from blockage and inflammation of sebaceous glands and hair follicles.

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A macule is a flat lesion with color change only.

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Urticaria refers to transient, itchy wheals (hives).

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The stratum corneum forms a tough, protective outer layer.

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Hyperhidrosis means abnormally increased sweating.

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The hypodermis connects skin to deeper structures.

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Contraction of arrector pili muscles produces goosebumps

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Papules are small, solid, raised skin lesions

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Sebum reduces water loss and keeps skin flexible.

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Langerhans cells are antigen-presenting cells involved in immune surveillance.

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Basal cell carcinoma originates from basal cells of the epidermis.

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Psoriasis is an immune-mediated chronic inflammatory skin disorder.

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Melanoma is a dangerous skin cancer derived from melanocytes.

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Stratum lucidum is present only in thick skin (palms and soles).

Explanation:
ABCDE evaluates asymmetry, border, color, diameter, and evolution of pigmented lesions.

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Blisters form when fluid accumulates between separated epidermal layers.

Explanation:
Fibroblasts produce collagen, essential for tissue repair.

Answer: B
Explanation: Vitiligo results from autoimmune destruction of melanocytes.

Explanation:
Sustained pressure reduces blood flow, leading to tissue necrosis.

The skin converts precursors into vitamin D under UV light, functioning as an endocrine organ.