Integumentary Disorders, Burns, and Wound Complications

1. Normal function first

The skin has three layers. The epidermis is the thin, outer, waterproof layer of tightly packed cells (keratinocytes) that constantly shed and renew. The dermis below it holds collagen and elastin fibers, blood vessels, nerves, hair follicles, and sweat and oil glands. The subcutaneous (hypodermis) layer stores fat and anchors skin to deeper tissue. The skin's barrier function comes mainly from the epidermis: it prevents water loss, blocks entry of microbes and chemicals, and shields against ultraviolet light. The skin is also the body's main thermoregulation organ — blood vessels in the dermis widen (vasodilate) to release heat or narrow (vasoconstrict) to conserve it, while sweat evaporation cools the body.

2. What changes in disease

• Pressure injuries: Sustained pressure on skin over a bony prominence compresses capillaries, starving tissue of oxygen. The damage starts deep and spreads outward, progressing from non-blanchable redness to open sores and, in severe cases, down to muscle and bone. Moisture, friction, and shearing (skin sliding one way while bone slides another) worsen it.
• Dermatitis: Inflammation of the skin ("-itis" = inflammation, "derm-" = skin) from irritants, allergens, or other triggers. The epidermis becomes red, itchy, swollen, and sometimes blistered or cracked, weakening the barrier.
• Psoriasis: A chronic condition in which skin cells multiply much faster than normal and the immune system drives inflammation, so thick, scaly, silvery plaques build up instead of shedding normally.
• Skin infections: Bacteria (such as Staphylococcus or Streptococcus), viruses, or fungi invade when the barrier is breached, causing cellulitis, abscess, impetigo, or other local infection that can spread.
• Burns: Thermal, chemical, electrical, or radiation injury destroys skin cells and damages the capillaries beneath. Burn-depth classification ranges from superficial (epidermis only, red and painful, heals without scarring) to partial-thickness (into the dermis, blistering) to full-thickness (through the dermis, may be painless because nerve endings are destroyed).
• Fluid shift: In major burns, damaged capillaries leak plasma (fluid and protein) into surrounding tissue, causing massive swelling (edema) and a drop in circulating blood volume. This "third-spacing" peaks in the first day or two.
• Infection risk: With the barrier gone and dead tissue present, bacteria colonize easily, and the body's immune defenses are impaired.
• Thermoregulation loss: Burned skin cannot retain heat or sweat normally, so the person loses heat and fluid rapidly.
• Wound dehiscence and infection: A healing wound can split open (dehiscence) if tension is too high or healing is poor, and any open wound can become infected, delaying closure.
• Scar formation: Healing by collagen deposition replaces normal tissue with scar tissue — stronger but less flexible, without hair follicles or sweat glands, and sometimes overgrown (hypertrophic or keloid).

3. Why the changes matter

A broken barrier leads to fluid and heat loss, infection, pain, and impaired mobility or body-image distress. Major burns can cause hypovolemic shock from fluid shift, hypothermia, and sepsis from infection. Pressure injuries signal poor tissue perfusion and can progress silently to deep, hard-to-heal wounds. Chronic skin inflammation (dermatitis, psoriasis) impairs quality of life and raises infection risk through scratching and cracking. Understanding these patterns guides assessment: measuring burn size and depth, checking skin over pressure points, watching fluid balance and temperature, and monitoring wounds for the redness, warmth, swelling, or drainage that may indicate infection.

How it works

1. Heat or another injury destroys skin cells and damages the small blood vessels in the dermis.
2. Those damaged capillaries become leaky, so plasma and protein escape into surrounding tissue, producing swelling.
3. Because that fluid left the bloodstream, the circulating blood volume falls, which can reduce blood pressure and delivery of oxygen to organs.
4. The damaged skin can no longer hold heat or block microbes, so heat is lost and infection risk rises while the body simultaneously tries to heal the wound.

Common confusions

Memory aids

"Barrier, Blood flow, Bugs" — the three B's of skin. A wound loses the Barrier, the Blood flow (or leaks it out), and invites Bugs (infection). For burn depth, think "S-P-F": Superficial (pink/painful), Partial (blisters), Full (waxy/leathery, may be numb).

Quick review

Topic Recap

• Skin is a layered, living barrier that manages water, microbes, and temperature.
• Pressure injuries, dermatitis, and psoriasis each disrupt skin through ischemia, inflammation, or overproduction of cells.
• Burns are classified by depth; major burns cause a life-threatening fluid shift, heat loss, and infection risk.
• Wound healing replaces damaged tissue with scar; infection and dehiscence are the key local complications.

Knowledge Check

1. Which layer of skin is primarily responsible for waterproofing and the microbial barrier?
2. Why can a full-thickness burn be less painful than a partial-thickness burn?
3. What is the fluid shift, and why is it dangerous after a major burn?
4. Why do pressure injuries often show deeper damage than is visible on the surface?
5. What is wound dehiscence, and what are two factors that increase its risk?

Answers and Rationales

1. Answer: The epidermis. Why: Its tightly packed keratinocytes and intercellular lipids keep water in and microbes out; the dermis supports and supplies but is not the main barrier.
2. Answer: Because a full-thickness burn destroys the nerve endings in the dermis, so sensation is lost. Why: Pain requires intact nerves; their destruction explains why the deepest burns can be numb while partial-thickness burns are intensely painful.
3. Answer: Damaged capillaries leak plasma and protein out of the bloodstream into the tissues, lowering circulating blood volume. Why: This can progress to hypovolemic shock and poor organ perfusion if large enough.
4. Answer: Pressure compresses the deep capillaries over the bone first, so tissue death begins below the surface and only later becomes visible on top. Why: The damage travels upward from the deep, compressed tissue.
5. Answer: Dehiscence is the reopening of a wound along the healing line. Why: High tension on the wound and infection (or poor nutrition/perfusion) are common contributors that weaken the repair.