3.3 Skin: Wound Healing

Flashcards covering key vocabulary related to epidermal and deep wound healing processes, including phases, cellular components, and types of scars.

Epidermal wound healing

The process your body uses to repair minor surface injuries that affect only the epidermis, the outermost layer of your skin.

Key Events and Cell Behavior in Epidermal Wound Healing:

• Key events and cell behavior:

  • Basal cells at the wound edge detach from the basement membrane, enlarge, and migrate across the wound to cover the exposed area.

  • Migration continues until cells from opposite sides meet in the middle.

  • Contact inhibition stops further movement once opposing sides meet.

  • After the wound is covered, epidermal growth factor (EGF) stimulates basal cells to divide, replacing migrated cells and rebuilding multiple epidermal layers.

• Outcomes:

  • Process is relatively fast.

  • No bleeding or scarring occurs because the dermis and underlying blood vessels are not damaged.

Contact inhibition

A mechanism that tells migrating cells to stop moving once they meet in the middle of a wound.

Deep wound healing

A more complex and longer healing process for injuries that go through the dermis or even deeper, affecting multiple layers. (eg, cuts, punctures, surgical wounds) The healing process for injuries that penetrate deeper than the epidermis and dermis, requiring more extensive repair. It involves four main phases: inflammatory, migratory, proliferative, and maturation.

• Definition: Occurs when an injury goes through the dermis or deeper (e.g., cuts, punctures, surgical wounds).

• Complexity and duration: Involves multiple tissue layers; the healing process is more complex and longer than epidermal wound healing.

• Four phases: inflammatory, migratory, proliferative, and maturation (remodeling).

Inflammatory phase (deep wound healing)

The first phase where blood vessels rupture, a blood clot forms to stop bleeding, and immune cells like neutrophils and macrophages clean up the wound.

• Immediate response: Blood vessels rupture at the injury site, triggering a blood clot that stops bleeding and seals the wound by bringing edges together.

• Signs of inflammation: Redness, swelling, heat, and pain due to dilation of blood vessels and increased blood flow.

• Cellular players: White blood cells, including neutrophils and macrophages, help clean up pathogens, damaged cells, and debris.

Migratory phase (deep wound healing)

The second phase where the clot hardens into a scab, fibroblasts produce scar tissue, damaged blood vessels regenerate, and granulation tissue forms.

• Clot evolution:

  • The initial clot hardens into scab, protecting the wound.

• Cellular activity:

  • Fibroblast migrate into the area and begin producing scar tissue made of collagen fibers and glycoproteins.

• Vascular changes:

  • Damaged blood vessels begin to regenerate.

• Tissue formation:

  • The clot is gradually replaced by granulation tissue, a soft pink, bumpy tissue that fills the wound.

Fibroblasts

Cells that migrate into a wound area and start producing scar tissue made of collagen fibers and glycoproteins.

Maturation or Remodeling phase (deep wound healing)

The forth and final phase where the scab falls off, collagen fibers reorganize to increase strength, fibroblasts decrease, and capillaries restore to normal, which can take weeks to months.

• Scab removal:

  • The scab falls off as healing progresses.

• Epidermis restoration:

  • The epidermis returns to its normal thickness.

• Collagen remodeling:

  • Collagen fibers reorganize along tension lines to increase tissue strength.

• Cellular and vascular changes:

  • Fibroblasts decrease in number; capillaries return to normal levels.

• Timeframe:

  • Remodeling can take weeks to months depending on injury severity.

Scar Formation and Fibrosis

Definition: The formation of scar tissue during healing is called fibrosis.

Scar quality:

• If healing is efficient, the scar is flat and pale.

• Excess collagen can lead to a hypertrophic scar (raised above the normal surface).

• If scar tissue grows beyond the wound's original boundaries, it is called a keloid scar.

• Functional differences of scar tissue:

  • Scar tissue lacks many normal skin features such as glands and hair follicles and does not have full strength and flexibility, making it functionally different from uninjured skin.

• Conceptual takeaway:

  • Wound healing demonstrates the body’s capacity to repair itself and is guided by precise cellular signals and cooperation between tissues.

Hypertrophic scar

A scar that is raised above the normal epidermal surface due to excess collagen.

Keloid scar

A hypertrophic scar that grows beyond the wound's original boundaries.

Scar tissue

Tissue that lacks many of the original skin features such as glands, hair follicles, and full strength and flexibility, making it functionally different from normal skin.

Proliferative Phase (deep wound healing)

The third phase. Is characterized by the formation of new collagen and blood vessels, leading to wound closure.

• Rebuilding processes ramp up:

  • Epithelial cells proliferate beneath the scab to cover the wound.

  • Fibroblasts continue laying down collagen to strengthen the tissue.

• Vascular support:

  • Capillaries grow into the area to meet high metabolic needs of healing cells.

• Visual outcome:

  • The wound begins to visibly shrink and fill in.