Factors Affecting Tissue Healing

Wound Contraction and Strength:

The wound starts contracting after 2-3 days and the process is completed by the 14th day. During this period, the wound is reduced by approximately 80% of its original size.

Contracted wound results in rapid healing since lesser surface area of the injured tissue has to be replaced.

Read And Learn More: General Pathology Notes

The wound is strengthened by proliferation of fibroblasts and myofibroblasts which get structural support from the extracellular matrix (ECM). In addition to providing structural support, ECM can direct cell migration, attachment, differentiation and organisation.

ECM is not a static structure but the matrix proteins comprising it undergo marked remodelling during foetal life which slows down in adult tissues. These matrix proteins are degraded by a family of metalloproteinases which act under the regulatory control of inhibitors of metalloproteinases.

ECM has five main components: collagen, adhesive glycoproteins, basement membrane, elastic fibres, and proteoglycans.

In wound healing, the deposition of proteoglycans precedes the laying of collagen. The strength of the wound also depends upon certain factors such as the site of injury, depth of incision and area of wound. After removal of stitches on around 7th day, the wound strength is approximately 10% which reaches 80% in about 3 months.

Factors Influencing Tissue Repair:

While several local and general factors delay wound healing, certain therapeutic influences stimulate healing.

1. Local Factors:

The following factors acting locally delay wound healing:

• Infection is the most important factor acting locally that delays the process of healing.
• Poor blood supply to wounds and ischaemia slow healing e.g. injuries to the face heal quickly due to rich blood supply while injury to leg with varicose ulcers having poor blood supply heals slowly.
• Foreign bodies including sutures interfere with healing and cause intense inflammatory reactions and infection.
• Movement delays wound healing.
• Exposure to ionising radiation delays granulation tissue formation.
• Exposure to ultraviolet light facilitates healing.
• Type, size and location of injury determine whether healing takes place by resolution or organisation.

2. General Factors:

A few general factors influence healing:

• Age Wound healing is rapid in young and somewhat slow in aged and debilitated people due to poor blood supply to the injured area in the latter.
• Nutrition Deficiency of constituents like protein, vitamin C (scurvy), vitamin A and zinc
  delays the wound healing.
• Systemic infection delays wound healing.
• Administration of glucocorticoids and NSAIDs delays wound healing.
• Uncontrolled diabetics are more prone to develop infections and hence delayed healing of
  wounds.
• Haematologic abnormalities like defects of neutrophil functions (chemotaxis and phagocytosis), and neutropenia and bleeding disorders slow the process of wound healing.
• Colder temperature delays healing.

3. Therapeutic Influences:

If there is delayed healing, appropriate therapy may be employed which stimulates healing by more efficient response but does not change the natural process of healing. Therapy works by influencing the chemical environment of the repair tissue to bring healing back on track if there is delayed healing but therapy is not indicated if the healing is proceeding normally.

These include the use of exercise therapy, manual therapy, electrotherapy etc. Besides, all local and general factors listed above which may delay healing should be attended and corrected, wherever possible.

Tissue Repair: Regeneration and Repair:

• Tissue repair or healing is the body’s response to injury in an attempt to restore normal structure and function by living tissue.
• It involves 2 processes: Regeneration and Repair.
• Regeneration is restoration to original tissue by the proliferation of surrounding undamaged specialised cells while repair is healing by formation of granulation tissue resulting in fibrosis and scarring.
  • Regeneration depends upon the dividing ability of parenchymal cells. Labile cells continue to divide throughout life (cough (due to tracheal compression by mediastinal lymphadenopathy) and dyspnoea are common.
  • Epidermis, mucosa), stable cells decrease or lose their ability to proliferate (cough (due to tracheal compression by mediastinal lymphadenopathy) and dyspnoea are common.
  • Liver, kidneys) while permanent cells cease to regenerate around the time of birth (e.g. neurons, myocardium).
• Repair is healing by formation of granulation tissue. It involves initial inflammatory reaction by the body, followed by clearance by proteolytic enzymes, and phase of angiogenesis and proliferation of fibroblasts.
  • The wound is strengthened by the proliferation of fibroblasts and myofibroblasts which get structural support from the extracellular matrix (ECM).
  • ECM is comprised by collagen, adhesive glycoproteins, basement membrane, elastic tissue and proteoglycans.
  • Various local and general factors may delay wound healing. Electrotherapy, exercise therapy and manual therapy are helpful to stimulate healing back on track if there is delayed healing.