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Structure

Skin

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The skin is the largest organ of the body and forms the integument with its appendages (hair, nails, glands). It provides a barrier against water loss, microbes and trauma, and contributes to sensation, thermoregulation and vitamin D synthesis.

Terminologia Anatomica (Latin): Cutis; Integumentum commune · Open in the 3D atlas

Location

It covers the whole external surface and is continuous with mucous membranes at the orifices. Thickness varies by region: thick on the palms and soles, thin on the eyelids.

Structure

Three layers: the epidermis (keratinised stratified squamous epithelium with strata basale, spinosum, granulosum, and corneum, plus lucidum in thick skin), the dermis (papillary and reticular layers) and the hypodermis (subcutaneous fat). Cells include keratinocytes, melanocytes, Langerhans cells and Merkel cells; appendages are hair follicles, sebaceous, eccrine and apocrine glands, and nails.

Blood supply

Perforating branches from underlying muscular and fascial arteries form a deep (subdermal) and a superficial (subpapillary) arterial plexus, with capillary loops in the dermal papillae. The epidermis has no vessels and is nourished by diffusion; cutaneous vessels also regulate heat loss.

Innervation

Cutaneous branches of spinal and cranial nerves supply defined dermatomes with overlap. Sensory receptors include free nerve endings, Meissner and Pacinian corpuscles, Ruffini endings and Merkel discs; sympathetic fibres supply sweat glands (cholinergic), arrector pili muscles and vessels.

Function

The skin forms a mechanical and immune barrier, limits transepidermal water loss, protects against ultraviolet radiation through melanin, regulates temperature by sweating and vasomotion, mediates touch, pain and temperature sensation, and synthesises vitamin D from 7-dehydrocholesterol under ultraviolet B.

Clinical correlations

Burns are classified by depth (superficial, partial-thickness, full-thickness); body surface area is estimated, for example by the rule of nines, with adjustments in children. Pressure ulcers arise over bony prominences. Melanoma is suspected from asymmetry, border, colour, diameter and evolution (ABCDE). Herpes zoster follows a single dermatome.

Common exam points

  • Layers from outside in: stratum corneum, lucidum (thick skin), granulosum, spinosum, basale; then dermis and hypodermis.
  • The epidermis is avascular; the dermis contains vessels, nerves, glands and follicles.
  • Melanocytes lie in the basal layer; Langerhans cells are antigen-presenting cells of the epidermis.
  • Burn depth determines healing and need for grafting; assess area and depth, and follow local burn protocols.
  • Dermatomal distribution of the rash points to herpes zoster.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Pawlina W. Histology: A Text and Atlas. Wolters Kluwer, 8th edition (2020) — Tier 3 (textbook)

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