Basic Principles Involved In Wound Healing

Basic Principles Involved in Wound Healing

Wound healing is a complex and dynamic process. Physiology of wound healing involves various phases such as hemostasis, inflammation, proliferation and maturation. A wound can occur due to various reasons. In order to understand basic principles involved in wound healing we need to understand layers of the skin first. In this article we will discuss about structure of skin, types of wounds, types of wound healing, basic principles of wound healing and factors affecting wound healing.

Table of Contents

Structure of Skin

Skin is the largest organ of human body having surface area of about 1.5 to 2 m² in adults. It covers the whole body and protects the underlying structures from injury and invasion by microbes. Skin contains the sensory (somatic) nerve endings of pain and involved in the regulation of body temperature. Skin contains various glands, hairs and nails. Underlying structures are separated by subcutaneous fat. Structure of skin is mainly composed of two layers epidermis and dermis.

Epidermis: It is the outermost layer and composed of stratified keratinized squamous epithelium tissue. Epidermis does not contain blood vessels and nerve endings. Its deeper layers contain interstitial fluids which supplies oxygen and nutrients.
Dermis: Dermis is the tough and elastic layer beneath epidermis layer. It is composed of connective tissue. Deepest layer contains areolar tissue and adipose tissue (fat). Dermis consist of blood vessels, lymph vessels, somatic nerve endings, sweat glands, hairs and sebaceous glands.

A skin wound results when there is a rupture in epidermis. Process of wound healing starts immediately after injury to epidermis and may last for few hours to years.

Types of Wounds

Any damage to the integrity of biological tissue is considered as wound. Depending on the appearance of wound it can be divided into two types as open wound and closed wound.

Open wound: In this case surface of skin is separates apart or split and the underlying structures are exposed to outer environment.
Closed Wound: In this type of wound the surface of skin is intact but underlying tissues may get damaged causing inflammation.

Wounds can also be classified according to their condition and cleanliness as illustrated in below table.

Type of Wound	Condition of Wound
Class I	· Clean · Uninfected · No inflammation · Mostly closed wound · Do not enter into respiratory, alimentary, genital or urinary tracts.
Class II	· Clean-contaminated · Lack unusual contaminations · Enters into the respiratory, alimentary, genital or urinary tracts.
Class III	· Contaminated · Fresh and open wounds · Caused by mis practice in sterile techniques or by GIT leakage into the wound
Class IV	· Dirty infected · Occurs due to improperly cared for traumatic wounds · Affected area is devilized tissue

Conditions required for wound healing

Process of wound healing involves two factors, one is systemic factors and another is local factors.

Systemic factors: Medical status of individual and nutritional status affects the process of wound healing. Infections, impaired immunity, poor blood supply, diabetes mellitus and cancer reduce rate of wound healing.

Local factors: Good blood supply to the affected site provides oxygen and nutrient, also removes waste products. Hence rate of wound healing increases.

Types of wound healing

Depending on the cause of wound and healing time, wounds can be classified in three types.

Type of wound	Condition of wound
Primary healing or primary intention	Uncomplicated, Non-infected, Well-approximated
Secondary healing or secondary intention	It begins when disrupted by infection, hypoxia or immune dysfunction, Formation of granulation tissue
Tertiary healing or third intention	Occurs when secondary intention is interrupted, May happen after granulation tissue has form, It is delayed primary wound healing after 4-6 days.

Basic principles of wound healing

The basic principles of wound healing involve four continuous and overlapping phases, hemostasis, inflammation, proliferation, maturation.

Basic Principles Involved in Wound Healing

Hemostasis

This phase starts when blood leaks out of the body and ends with formation of blood clot.
Blood vessels constrict to reduce blood flow.
Platelets get aggregated and stick to the sub-endothelium surface within blood vessels epithelial wall.
After about one minute, the first fibrin strands begin to adhere.
After the formation of fibrin mesh, liquid blood transforms into gel through coagulants and release of prothrombin.
Formation of clots (thrombus) keep platelets and blood cells trapped in wound area.
If thrombus gets detached from vessel wall, it goes through the circulatory system causing stroke, pulmonary embolism or heart attack.

Inflammation

It starts immediately after injury when injured blood vessels leak water, salt and protein, which causes localized swelling.
Inflammation controls bleeding and prevents infection.
The fluid engorgement promotes healing and repair cells to move to the site of wound.
In this phase damaged cells, pathogens and microbes are drained from wound area,
Inflammation is natural part of wound healing and it becomes problematic only if prolonged or excessive.

Proliferation (granulation and contraction)

This phase starts when the wound is rebuilt with new tissue made up collagen and extracellular matrix.
The wound contracts due to formation of new tissue.
Oxygen and nutrients are provided to newly built granulation tissue by constructing a new network of blood vessels.
The action of myofibroblast causes the wound to contract by gripping the ages of wound and pulling them together.
Healthy granulation tissue is pink or red, uneven in texture and does not bleed easily. Dark granulation tissue may be sign of infection, ischemia or poor perfusion.
In final stage epithelial cells resurface the injury. This stage happens faster when wounds are kept moist and hydrated.

Maturation (remodeling)

In this stage collagen is remodeled from type III to type I and wound gets closed. This conversion is facilitated by enzyme metalloproteinase secreted by fibrinoblast.
The cells used in the process of wound repair are removed by apoptosis or programmed cell death.
Collagen is remodeled into more organized structure which increases the tensile strength of healing tissue.
The remodeling stage begins after about 21 days of injury and can continue for years.
Even after complete wound healing, the healed area becomes weaker than normal skin. Generally having 80% of tensile strength compared to unwounded skin.

factors affecting wound healing

Age of person
Presence of chronic disease
Type of wound
Location of wound
Lack of nutrition
Patient behavior (addiction)
Presence of edema
Poor blood circulation
Medication

Conclusion

Wound healing is a natural phenomenon. Wound healing is a process where our body repair itself after injury. There are different types of wounds like open and closed wounds. Understanding of them helps to provide right care at right time. Healing stages play a crucial role in rebuilding tissue and restoring strength. There are four stages of wound healing, hemostasis, inflammation, proliferation and maturation. There are various factors which affects wound healing process such as age, nutrition, chronic illness and medication. Recognition of these factors helps to cure wound fast.