Wound Healing

Objective

At the end of this PDF, student will be able to

•         Define “Healing”

•        Describe the processes involved in healing

•        Describe the contraction of wound

•        Explain the process of healing of wound of skin

Wound Healing

Wound healing is a remarkable process that our bodies undertake whenever we suffer an injury. From minor cuts and scrapes to surgical incisions and more severe wounds, our bodies have a remarkable ability to repair damaged tissue and restore normal function.

Types of Wounds

Wounds are generally categorized into two types:

• Acute Wounds: These are typically caused by a single, traumatic event and tend to heal quickly.
• Chronic Wounds: Chronic wounds are more complex and can be the result of underlying health issues. They often require specialized care and a longer healing process.

Healing

•       Healing – body response to injury

•       An attempt to restore normal structure and function

•       Involves 2 distinct processes:

•       Regeneration – healing by proliferation of parenchymal cells; results in complete restoration

•       Repair – healing by proliferation of connective tissue elements resulting in fibrosis and scar

Regeneration

•       Proliferation of parenchmal cells

•       Complete restoration of original tissue

•       Cells are under the constant regulatory control of their cell cycle

•       Involves

–       Epidermal growth factor

–       fibroblast growth factor, platelet derived

–      growth factor, endothelial growth factor,

–      transforming growth factor-β

The Stages of Wound Healing

Wound healing occurs in four distinct stages, each with its specific characteristics and requirements:

1. Hemostasis: This is the initial stage where the bleeding is stopped. Platelets form a plug to seal the wound, and blood vessels constrict.
2. Inflammation: Inflammation is a necessary part of the healing process. It helps remove foreign particles and prepares the wound for repair.
3. Proliferation: In this stage, new tissue is formed to replace the damaged area. Collagen, a protein that provides strength, is synthesized.
4. Remodeling: The final stage involves the strengthening and remodeling of the newly formed tissue, improving its durability.

Cell cycle and its phases

•       Period between two successive cell divisions

•       M (mitosis) phase: Phase of mitosis.

•       G1 (gap 1) phase: daughter cell enters G1 phase after mitosis

•       S (synthesis) phase: the synthesis of nuclear DNA

•       G2 (gap 2) phase

•       G0 (gap 0) phase: resting phase of the cell after an M phase

Phases of cell cycle

Type of cells involved in regeneration – depending on the speed of cell division

•       Labile cells – continuously dividing

•       Epidermis, mucosal epithelium, GI tract epithelium etc

•       Stable cells – low level of replication

•       Hepatocytes, renal tubular epithelium, pancreatic acini

•       Permanent cells – never divide

•       Nerve cells, cardiac myocytes, skeletal muscle

Tissue Repair

•       Replacement of injured tissue by fibrous tissue

Two processes are involved in repair:

1. Granulation tissue formation

2. Contraction of wounds

•       Involves mesenchymal cells

•       connective tissue cells

•       endothelial cells, macrophages & some
parenchymal cells

Granulation tissue formation

Phase of inflammation

•       Acute inflammatory

•       Response with exudation of plasma, neutrophils

•       Monocytes within 24 hours

Phase of clearance

•       Proteolytic enzymes liberated from Neutrophils

•       Autolytic enzymes from dead tissues cells

•       Phagocytic activity of macrophages

•       Clear off the necrotic tissue, debris and RBCs

Phase of ingrowth of granulation tissue

1.      Angiogenesis

•      Proliferation of endothelial cells

•      Development of capillary sprout

•      Vascular endothelial growth factor (VEGF)

•      Platelet-derived growth factor (PDGF)

2. Fibrogenesis

•         Fibroblasts originate from fibrocytes

•         Collagen fibrils begin to appear by about 6th day

•         Formation of inactive looking scar – cicatrisation

Contraction of wounds

•       Wound starts contracting after 2-3 days

•       Process is completed by the 14th day

•       Reduced by approximately 80% of its original size

•       Results in rapid healing

•       Dehydration

•       Contraction of collagen

•       Appearance of Myofibroblasts

Healing of wounds in the skin

•       Combination of Regeneration and repair

Accomplished in one of the following two ways:

Ø  Healing by first intention (primary union)

Ø  Healing by second intention (secondary union)

Healing by first intention (primary union)

Characteristics

•       Clean and uninfected

•       Surgically incised

•       Without much loss of cells and tissue

•       Edges of wound are approximated by surgical sutures

Sequence of events

•       Initial haemorrhage

•       Acute inflammatory response

•       Epithelial changes

•       Organisation

•       Suture tracks

Healing by first intention

Healing by second intention (secondary union)

Characteristics

•       Open with a large tissue defect, at times infected

•       Having extensive loss of cells and tissues

•       The wound is not approximated by surgical sutures but is left open

Sequence of events

•       Initial haemorrhage followed by clotting

•       Inflammatory phase – neutrophills & macrophages

•       Epithelial changes – epidermal cell margination & proliferation

•       Granulation tissue

•       Wound contraction

Factors Affecting Wound Healing

Local factors

•       Infection

•       Blood supply to wound area

•       Mechanical factors

•       Foreign bodies

•       Exposure to ionising radiation

•       Size, Location & type of wound

Systemic factors

•       Age

•       Nutrition

•       Systemic infection

•       Uncontrolled diabetes

•       Haemetological abnormalities

Summary

•       Healing is a body response to injury it is an  attempt to restore normal structure and function

•       Healing occurs by two processes- regeneration and repair

•       Contraction of wound involves dehydration, contraction of collagen, appearance of myofibroblasts

•       Healing of wounds of skin occurs by first intention or second intention depending on the type of infection