Integumentary System: Tissue Repair, Wound Healing, Haemostasis, Skin Cancer, and Burns

Tissue Repair and Wound Healing

Overview of Tissue Repair

Tissue repair is a fundamental process in the integumentary system, involving the restoration of tissue structure and function after injury. It occurs through two main mechanisms: regeneration and replacement by connective tissue.

• Regeneration: Injured tissue is replaced by stem cells of the original tissue, restoring normal structure and function. Example: hepatocytes in the liver.

• Replacement (Fibrosis): Injured tissue is replaced by connective tissue, resulting in scar formation. This occurs when cells cannot divide, such as in cardiac muscle.

• Combined Processes: Both regeneration and fibrosis often occur together, but in some tissues (e.g., cardiac muscle), only fibrosis is possible.

Phases of Wound Healing

Wound healing is a complex process involving several overlapping phases:

1. Inflammation: Blood clot forms, inflammatory chemicals are released, and immune cells migrate to the site.

2. Organization: Restoration of blood supply, formation of granulation tissue, and migration of fibroblasts.

3. Regeneration and Fibrosis: Epithelium regenerates, and fibrous tissue matures to form a scar.

Additional info: The diagram provided illustrates the stages of tissue repair, including the formation of a scab, migration of cells, and restoration of tissue integrity.

Healing by Primary and Secondary Intention

Primary Intention

Healing by primary intention occurs when wound edges are closely apposed, such as in surgical incisions.

• Minimal tissue loss and rapid healing.

• Low risk of infection and minimal scarring.

Secondary Intention

Healing by secondary intention occurs when wound edges are not closely apposed, often due to extensive tissue loss.

• Greater tissue loss and slower healing.

• Higher risk of infection and more prominent scarring.

• Granulation tissue formation is more extensive.

Dysfunctional Wound Healing

Inflammatory Phase Dysfunction

Problems during the inflammatory phase can lead to impaired healing.

• Hemorrhage: Excessive bleeding at the wound site.

• Adhesion formation: Abnormal fibrous connections between tissues.

• Infection and sepsis: Microbial invasion delays healing and increases risk of systemic infection.

• Hypovolaemia: Reduced blood volume impairs tissue perfusion.

Reconstructive Phase Dysfunction

• Impaired collagen synthesis: Leads to abnormal scarring, such as keloid or hypertrophic scars.

• Impaired epithelialization: Delayed reformation of the epithelial layer due to anti-inflammatory steroids, hypoxaemia, or nutritional deficiencies.

• Impaired contraction: Results in contractures, commonly seen in burn injuries.

• Wound disruption (Dehiscence): Wound pulls apart at the suture line, often due to excessive strain or obesity, increasing risk of wound sepsis.

Haemostasis

Definition and Phases

Haemostasis is the process of arresting bleeding following vascular injury. It involves three main phases:

1. Vascular Spasm: Immediate vasoconstriction reduces blood flow.

2. Platelet Plug Formation: Platelets adhere to the site of injury and aggregate to form a temporary plug.

3. Coagulation: A cascade of clotting factors leads to the formation of insoluble fibrin threads, stabilizing the clot.

Coagulation Pathways

• Intrinsic Pathway: Triggered by damage within the blood vessel; involves factors XII, XI, IX, VIII.

• Extrinsic Pathway: Triggered by tissue factor released from injured tissue; involves factor VII.

• Both pathways converge at the activation of factor X, leading to the conversion of prothrombin to thrombin and fibrinogen to fibrin.

Key Equations:

• $\text{Prothrombin} \xrightarrow{\text{Thrombin}} \text{Fibrinogen} \rightarrow \text{Fibrin}$

• $\text{Intrinsic and Extrinsic Pathways} \rightarrow \text{Activation of Factor X}$

Additional info: Platelet aggregation is facilitated by von Willebrand factor released from endothelium.

Skin Cancer

Types of Skin Cancer

Skin cancer arises from different cell types within the epidermis and has varying risk factors and clinical manifestations.

• Basal Cell Carcinoma (BCC): Originates from stem cells in the basal layer of the epidermis. Associated with repeated UVB exposure. Presents as superficial, nodular, or morphoeic lesions. Treatment: Surgical excision, Mohs surgery, cryotherapy, topical creams, photodynamic therapy, radiotherapy.

• Squamous Cell Carcinoma (SCC): Arises from keratinocytes in the outer epidermis. Can affect skin and mucous membranes. Precursor lesion is solar keratosis. Risk factors: UVB, HPV infection, immunosuppression, smoking. Treatment: Usually surgical excision; non-invasive methods for superficial lesions.

• Malignant Melanoma: Originates from melanocytes. High metastatic potential. Risk factors: UVB exposure, sunburn (especially in childhood), fair skin, red or blond hair, presence of naevi. Treatment: Wide surgical excision, sentinel lymph node biopsy, adjuvant therapy.

Burns

Classification of Burns

Burn injuries are classified by cause, extent, and depth.

• Causes: Thermal, electrical, chemical, radiation.

• Extent: Assessed by the 'Rule of Nines' to estimate body surface area affected.

• Depth: Classified by degree (first, second, third), thickness (superficial, partial, full), and layers affected (epidermal, superficial dermal, mid-dermal, deep dermal, full thickness).

Burn Depth Assessment Table

The following table summarizes the characteristics of burns by depth:

Burn Depth	Appearance	Layers Affected	Sensation
Superficial	Dry and red, blanches with pressure	Epidermis only	Intact, painful
Superficial Dermal	Moist, red, blisters present	Epidermis + superficial dermis	Very painful
Mid-Dermal	Pale pink, less moist, some blisters	Epidermis + mid dermis	Painful, but less than superficial
Deep-Dermal	Pale, mottled, dry	Epidermis + deep dermis	Reduced sensation
Full Thickness	White, brown, or black, leathery	All skin layers	Absent sensation

Additional info: Table entries inferred from standard clinical descriptions of burn depth.

Treatment of Burns

• Airway management to ensure adequate oxygenation.

• Fluid resuscitation to prevent shock.

• Analgesia for pain control.

• Infection control to prevent sepsis.

• Nutritional support to aid healing.

• Wound management including debridement, grafting, and escharotomy.

• Management of complications such as contractures and scarring.