Skin Injury and Repair

When skin is injured, it can often repair itself, unlike some other organs like the heart or brain (to a limited extent).
The skin repair process involves three major phases: inflammation, repair, and potentially scarring.

Consider an injury that penetrates the epidermis and reaches the dermis, potentially damaging smaller blood vessels and various cells (e.g., stratified squamous epithelial cells, fibroblasts, sweat glands, hair follicles).
Damaged cells release inflammatory chemicals, signaling an SOS to the body.
These chemicals cause blood vessels in the injured area to dilate (vasodilation).
- Dilation increases nutrient-filled blood flow to promote healing.
- Increased blood flow also causes redness in the injured area.
Inflammatory chemicals also make blood vessels more permeable, leading to swelling.
- Tiny holes develop in the blood vessel walls, causing water (fluid from the blood) to leak out.
- This fluid helps flush pathogens and debris from the wound area, but also contributes to swelling.
White blood cells (leukocytes) also migrate out of the blood vessels through these holes.
- Leukocytes phagocytose bacteria and other pathogens in the wound area.
- This is a suicide mission for leukocytes; they die after consuming pathogens.
- Accumulation of dead leukocytes forms pus, particularly in infected wounds.
Pain is another component of inflammation.
- Inflammatory chemicals irritate nerve cells in the area.
- Irritated nerve cells transmit pain signals to the brain.
- Pain promotes immobility of the injured area, facilitating faster healing.
The three main signs of inflammation are redness (vasodilation), swelling (fluid leakage), and pain (nerve irritation).

After the area is cleared of pathogens (aided by the inflammation phase), the repair process begins.
Damaged blood vessels start to repair themselves, supported by the increased nutrient supply.
Leukocytes continue to clear debris, preparing the area for fibroblast activity.
Fibroblasts produce collagen, which acts to sew the edges of the wound together.
As collagen dries, it pulls the wound edges closer, closing the opening.
Epithelial cells then multiply to cover the wound surface.
If epithelial cells successfully cover the area, the wound may heal without a visible trace.
If epithelial tissue cannot completely cover the wound, collagen fibers fill the gap, resulting in a scar.
- Scars are often lighter in color because they lack melanocytes.
- A scar is essentially the dermis being exposed because there is no epithelial for cover.

Inflammation is the body's beneficial response to damage, promoting healing through chemical signals, vasodilation, fluid movement, and leukocyte activity.
Infection, on the other hand, is a harmful process where pathogens (bacteria, viruses, parasites) enter the body, reproduce, and cause further tissue damage due to unsuccessful inflammation.

Decubitus ulcers, or bedsores, are a type of injury that can occur in immobile patients, especially in nursing homes.
Prolonged pressure on certain areas (e.g., elbows, back, tailbone) compresses blood vessels.
Compression restricts blood flow, leading to cell death, starting with epithelial cells.
The damage progresses through layers of tissue (dermis, muscle) and can eventually reach the bone.
Stages of bedsores:
- Stage 1: damage to the epithelial tissue.
- Stage 2: damage to the connective tissue (dermis).
- Stage 3: damage to the muscle tissue.
- Stage 4: damage extending to the bone.
Healing is difficult once bedsores develop; prevention is key.
Prevention strategies include frequent repositioning of the patient and using specialized support surfaces (e.g., egg crate mattresses, water beds) to relieve pressure.
The initial sign of a bedsore is redness, as the body attempts to dilate blood vessels in the area.
However, continued compression leads to epithelial tissue damage, progressing deeper.
Necrosis (tissue death) can occur, and severe cases may require removal of dead tissue or even amputation to prevent gangrene.