Healing Processes and Cell Types

Study Notes

Regeneration: Replacement of lost tissue with similar tissue types.
Repair (Healing by Scarring): Replacement of lost tissue by granulation tissue, eventually forming a scar.

Tissue Damage → Inflammation → Removal of Dead Tissue & Injury Agent → Replacement:
- Replacement occurs by either specialized tissues (regeneration) or fibrous tissue (scarring).
- This leads to healing.

Labile Cells: Continuously turn over through stem cell division. Found in the surface epithelium of the gastrointestinal tract, urinary tract, and skin.
Stable Cells: Have a lower replication rate than labile cells but can rapidly divide in response to injury. Examples include liver cells, endocrine glands, and renal tubular epithelium.
Permanent Cells: Non-dividing cells. Replacement not possible if lost. Examples include adult neurons and lens cells.

Wound contraction is a mechanical process that reduces the size of a wound.
Wounds contract by 70-80% of their original size.
This process speeds up healing by decreasing the amount of damaged tissue needing replacement.
Preventing contraction leads to slow healing & a large scar.

Healing by First Intention (Primary Union):
- Occurs when a wound is clean, closed with sutures, and edges are approximate.
- The incision site is immediately filled, sealed and the area heals relatively quickly.
- A scab is often formed.
Healing by Second Intention (Secondary Union):
- Occurs with extensive tissue loss/damage.
- Large defects are created. Examples include infarctions, ulcers, abscesses, and severe surface wounds.
- Healing is more drawn out.

Wound Type, Size, and Location: Clean surgical incisions heal faster than wounds caused by blunt trauma.
Vascular Supply: Adequate blood flow is crucial for delivering oxygen and nutrients to the healing area.
Infection: Infections significantly delay or prevent healing.
Ionizing Radiation: Radiation harms tissue and slows down the healing process.

Circulatory Status: Poor circulation reduces the supply of nutrients and oxygen to the injured area.
Metabolic Status: Poorly controlled diabetes impairs blood circulation and sensation and delays healing. Diseases and conditions can disrupt the wound healing process.
Nutritional Deficiencies: Poor nutrition reduces healing speed and impairs wound repair processes.
Hormones (Corticosteroids): Corticosteroids can hinder wound healing. Other hormones such as thyroid, androgens, estrogens, and growth hormone influence wound healing as well.

Infection: Bacteria entering the wound site can cause delays, or stop healing completely.
Deficient Scar Formation: Results in conditions such as wound dehiscence (wound gap), incisions hernias, and ulcerations.
Excessive Scar Formation: Results in raised scars (keloids) which can recur periodically. Hypertrophic scars are similar to keloids, but do not recur after surgical excision.