The integumentary system includes the skin, hair, nails and cutaneous glands. Together these structures protect against environmental injury and excessive water loss, support temperature regulation, provide sensory information and participate in immune defence and vitamin D synthesis. Nurses need to understand the system because skin findings can reflect both local damage and systemic illness.
Learning outcomes
- Distinguish epidermis, dermis and hypodermis.
- Explain the roles of keratinocytes, melanocytes, immune cells and touch receptors.
- Trace the main phases of wound healing without confusing them with a clinical treatment protocol.
- Describe the structure of hair, nails and glands.
- Explain how pressure, shear and moisture threaten skin integrity.
1. Layers of the skin
Epidermis
The epidermis is the superficial, avascular layer. Most of its cells are keratinocytes, which differentiate and contribute to a water-resistant protective barrier. The principal layers of thick skin are stratum basale, spinosum, granulosum, lucidum and corneum, from deep to superficial. Thin skin generally lacks a distinct stratum lucidum. The basal layer contains proliferating cells; the outer cornified layer consists largely of flattened dead cells rich in keratin.
Melanocytes produce melanin and transfer pigment to keratinocytes, providing some protection against ultraviolet radiation. Epidermal immune cells contribute to surveillance, while specialised mechanosensory cells participate in touch perception. Skin colour, inflammation and injury may appear differently across skin tones, so assessment must not rely on redness alone.
Dermis
The dermis is a vascular connective tissue layer underlying the epidermis. Its papillary region is mainly loose connective tissue, whereas the deeper reticular region contains dense irregular connective tissue rich in collagen and elastic fibres. Blood vessels, lymphatics, nerves, hair follicles, sweat glands and sebaceous glands lie within or pass through the dermis. Its blood supply supports nutrient delivery, thermoregulation and repair.
Hypodermis (subcutaneous tissue)
The hypodermis is deep to the dermis and consists largely of loose connective and adipose tissue. It cushions structures, stores energy and helps insulate the body. Anatomically it is associated with the integumentary system but is not technically one of the two main layers of skin.
2. Epidermal layers at a glance
| Layer (deep to superficial) | Key feature | Learning point |
|---|---|---|
| Stratum basale | Mitotically active basal keratinocytes | Continual renewal and connection to basement membrane |
| Stratum spinosum | Cells linked by desmosomes | Mechanical cohesion |
| Stratum granulosum | Keratinisation and barrier formation | Limits water loss |
| Stratum lucidum | Translucent layer in thick skin | Prominent on palms and soles |
| Stratum corneum | Flattened cornified cells | Outer protective barrier |
3. Skin appendages
Hair follicles produce hair shafts; arrector pili muscles attach to follicles. Hair supports sensation and reduces friction in selected regions. Sebaceous glands release sebum into many hair follicles, helping lubricate skin and hair. Eccrine sweat glands are widely distributed and contribute strongly to temperature regulation through evaporative cooling. Apocrine sweat glands occur in specific regions, become active around puberty and are associated with hair follicles.
Nails are hard keratin plates produced primarily by cells of the nail matrix. The visible nail plate overlies the nail bed. Nail findings can prompt further assessment but should not be interpreted as a stand-alone diagnosis of nutritional, pulmonary or circulatory disease.
4. Skin sensation and temperature regulation
The skin contains receptors involved in light touch, pressure, vibration, temperature and nociception. Different receptors are specialised for different forms of mechanical stimulation; pain and temperature pathways also involve free nerve endings. During overheating, increased skin blood flow and sweating promote heat loss. In cold conditions, reduced cutaneous blood flow conserves core heat, although the balance varies with physiological and environmental conditions.
5. Wound healing: overlapping phases
- Haemostasis: vascular responses and clot formation help limit bleeding and produce a provisional matrix.
- Inflammation: immune cells remove debris and respond to microbes; normal early inflammation is not identical to infection.
- Proliferation: granulation tissue develops, new vessels form, and epithelial cells migrate to cover the wound surface; contraction may occur.
- Remodelling: collagen is reorganised and the scar matures over time. Repaired tissue may not recover the full mechanical strength of uninjured skin.
These phases overlap rather than occurring as perfectly separated steps. Healing may be affected by blood flow, diabetes, infection, nutrition, smoking, repeated mechanical stress and other patient-specific factors. The appropriate management of a wound depends on assessment and current clinical guidance.
6. Pressure, shear, friction and moisture
A pressure injury is localised damage to the skin and/or underlying tissues, commonly over a bony prominence or associated with a medical device. Pressure and shear can impair tissue viability; friction and excessive moisture may contribute to superficial skin damage or increase vulnerability. Assessment includes mobility, sensation, perfusion, skin condition, nutrition and device contact areas. A structured risk tool supports but does not replace professional judgement.
In patients with darkly pigmented skin, early injury may not present as easily visible redness. Consider local changes in temperature, firmness, pain or tissue appearance and compare with surrounding skin. Do not assume that absence of visible erythema means tissue is unharmed.
7. Worked student case
An older adult with limited mobility reports discomfort at the heel. A student should describe the anatomical site, observe skin colour relative to surrounding skin, note temperature, tenderness and any visible changes, and promptly report concerns through the clinical team. The student should not assume the tissue is healthy based solely on colour or classify an injury without supervised assessment. Explain how heel pressure, reduced mobility and impaired perfusion could interact without presenting them as a confirmed diagnosis.
8. Self-assessment questions and answers
- Which skin layer contains most blood vessels? Dermis.
- Is the hypodermis one of the two principal skin layers? No; it lies beneath the dermis.
- Which epidermal layer is distinctive in thick skin? Stratum lucidum.
- Which glands are central to evaporative cooling? Eccrine sweat glands.
- Are wound-healing stages completely separate in time? No, they overlap.
- Does absent visible redness exclude a pressure injury? No.
References
- OpenStax Anatomy and Physiology 2e, §5.1 Layers of the Skin.
- OpenStax, §5.2 Accessory Structures of the Skin.
- OpenStax, §5.5 Diseases, Disorders and Injuries of the Integumentary System.
- NICE guideline CG179, Pressure ulcers: prevention and management.
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