Integumentary System and Burn Pathology: Study Guide

Integumentary System

Core Skin Anatomy

The skin is composed of three main layers, each with distinct structures and functions. Understanding these layers is essential for recognizing how the skin protects the body and responds to injury.

• Epidermis: The most superficial layer; avascular and composed mainly of keratinocytes. Functions as a protective, waterproof barrier against pathogens and abrasion.

• Dermis: Located beneath the epidermis; contains blood vessels, nerves, sweat and sebaceous glands, hair follicles, collagen, and elastic fibers. Provides strength, elasticity, sensation, and thermoregulation.

• Hypodermis (Subcutaneous Layer): Deepest layer; consists of adipose and areolar connective tissue. Anchors skin, insulates, stores energy, and cushions underlying structures.

Epidermal Layers (Superficial to Deep)

The epidermis is stratified into several layers, each with specialized cells and functions:

• Stratum corneum: Outermost layer of dead, flattened, heavily keratinized cells; provides abrasion resistance and major protection.

• Stratum lucidum: Clear, translucent layer found only in thick skin (palms, soles).

• Stratum granulosum: Contains keratohyalin granules; cells release lipids and proteins, forming a hydrophobic barrier.

• Stratum spinosum: Cells appear spiky; contains Langerhans (immune) cells.

• Stratum basale (germinativum): Deepest layer; mitotically active stem cells attached to the basement membrane, producing new keratinocytes.

Dermal Layers

The dermis is divided into two layers:

• Papillary layer: Superficial, thin, areolar connective tissue with dermal papillae; nourishes the epidermis and forms fingerprints.

• Reticular layer: Deeper, thicker, dense irregular connective tissue; provides strength, elasticity, and houses glands, hair follicles, nerves, and blood vessels.

Hypodermis

The hypodermis is not technically part of the skin but is closely associated with it. It consists mainly of adipose tissue and areolar connective tissue, providing insulation, energy storage, and cushioning. It also contains larger blood vessels and nerves.

Skin Structure and Function: Key Questions

Labeling and Descriptions

• Major layers (superficial to deep): Epidermis, dermis, hypodermis.

• Epidermal sublayers (thin skin): Stratum corneum, stratum granulosum, stratum spinosum, stratum basale.

• Epidermal sublayers (thick skin): Includes stratum lucidum between corneum and granulosum.

• Dermal sublayers: Papillary layer (superficial), reticular layer (deep).

Thick vs. Thin Skin

• Thick skin: Found on palms and soles; has all five epidermal layers (including stratum lucidum), thicker stratum corneum, more sweat glands, lacks hair follicles and sebaceous glands.

• Thin skin: Covers most of the body; lacks stratum lucidum, contains hair follicles and sebaceous glands, thinner epidermis.

Nutrition and Cell Death in the Epidermis

• Oxygen and nutrients: The avascular epidermis receives nutrients by diffusion from dermal blood vessels. Cells farther from the dermis receive fewer nutrients, leading to cell death as they move toward the surface.

• Keratinization: As cells move upward, they fill with keratin, lose organelles, and become flattened, dead cells in the stratum corneum.

Burn Classification and Pathology

Burn Types and Characteristics

Burns are classified by depth and extent of tissue damage. The main types are:

Burn Type	Skin Layers Damaged	Characteristics	Potential Complications	Treatment
First-degree (superficial)	Epidermis only	Red, painful, dry, mild swelling; no blisters	Usually minor; peeling, mild dehydration if widespread	Cool water, pain relief, moisturize, sun protection
Second-degree (partial-thickness)	Epidermis and part of dermis	Red, swollen, painful, moist, blistering	Infection, fluid loss, scarring, pigment change	Cool water, sterile dressing, wound cleaning, pain control; medical care if large/deep
Third-degree (full-thickness)	Entire epidermis and dermis; may extend into hypodermis	White, brown, black, leathery, waxy or charred; may be painless in center	Severe fluid/electrolyte loss, infection, shock, contractures, scarring, impaired circulation	Emergency care, IV fluids, antibiotics, debridement, escharotomy, skin grafting

Burn Pathophysiology

• Full-thickness burn: Destroys the entire epidermis and dermis, possibly extending into the hypodermis. Impairs skin repair, sensation, and barrier function.

• Blister formation: In second-degree burns, increased capillary permeability allows fluid to separate epidermal layers, forming blisters.

• Healing: Full-thickness burns heal poorly due to destruction of stem cells and blood vessels; often require skin grafting.

• Pain: Third-degree burns may be painless in the center due to nerve destruction; second-degree burns are often more painful due to intact, irritated nerve endings.

Burn Complications

• Dehydration and electrolyte imbalance: Loss of the epidermal barrier allows fluid and electrolytes to escape, risking hypovolemia and shock.

• Infection: Loss of the skin barrier increases susceptibility to pathogens.

• Scarring and contractures: Healing by fibrosis can limit mobility and function.

Burn Assessment and Treatment

Rule of Nines

The rule of nines is used to estimate the percentage of total body surface area (TBSA) affected by burns:

Body Region	Percent of Body Surface Area
Head and neck	9% (anterior 4.5%, posterior 4.5%)
Each upper limb	9%
Trunk	36% (anterior 18%, posterior 18%)
Each lower limb	18% (anterior 9%, posterior 9%)
Genitalia/perineum	1%

• Example: Burns to anterior lower limbs (9% each), genitalia (1%), and anterior trunk (18%) = 37% TBSA.

• Hand burns: The palm of one hand ≈ 1% TBSA; dorsum of one hand ≈ 0.5–1%.

Burn Management

• Fluid and electrolyte replacement: Required for burns covering large TBSA to prevent shock.

• Antibiotics: Broad-spectrum antibiotics are used to prevent or treat infection in full-thickness burns.

• Escharotomy: Surgical incision through burned, non-elastic tissue (eschar) to relieve pressure and restore circulation.

• Elevation and ring removal: Elevating burned limbs reduces swelling; removing rings prevents circulatory compromise due to swelling.

Skin Grafting

Graft Type	Description	Pros	Cons	When to Use
Autograft	Skin from another site on the same person	Best long-term option; lowest rejection risk; permanent coverage	Requires donor site wound; limited by available healthy skin	Preferred for permanent treatment of full-thickness burns with enough healthy donor skin
Allograft	Skin from another human donor (often cadaver)	Useful temporary coverage; protects wound, decreases fluid loss	Can be rejected; usually temporary; disease-screening required	Used when immediate coverage is needed or insufficient donor skin for autograft

• Example: For a small hand burn, an autograft is preferred due to low rejection risk and permanent coverage.

Exam-Ready Summary

• Epidermis: Protective, waterproof, avascular outer layer.

• Dermis: Supports epidermis; contains blood vessels, nerves, glands, follicles.

• Hypodermis: Cushions, insulates, stores fat, anchors skin.

• First-degree burns: Affect only the epidermis.

• Second-degree burns: Affect epidermis and part of dermis; commonly blister.

• Third-degree burns: Destroy epidermis and dermis; may be painless in center due to nerve destruction.

• Severe burns: Can cause fluid loss, electrolyte imbalance, infection, and shock.

• Rule of nines: Estimates burn size for treatment planning.

• Elevation and ring removal: Reduce swelling and prevent circulatory restriction.

• Escharotomy: Relieves pressure from tight, burned tissue.

• Autograft: Preferred for permanent coverage when enough healthy donor skin is available.

Short-Answer Practice

• Why do severe burns cause dehydration? Severe burns destroy the epidermal waterproof barrier, allowing fluid and electrolytes to leak from the body, reducing blood volume and increasing risk of shock.

• Why can a third-degree burn be less painful than a second-degree burn? Third-degree burns can destroy sensory nerve endings, while second-degree burns often leave irritated nerve endings intact.

• Why is infection a major concern after burns? Skin normally prevents pathogen entry; burns destroy this barrier and expose damaged tissue, increasing infection risk.

• Why do second-degree burns blister? Inflammation increases capillary permeability, and fluid collects between damaged skin layers, forming blisters.

• Why is an autograft preferred over an allograft? An autograft uses the patient's own tissue, so rejection risk is much lower and the graft can provide permanent coverage.