Metabolism and environment in the wound
The wound healing process is accompanied by pronounced changes in the internal environment within the damaged area. Due to anaerobic glycolysis and impaired blood flow, lactic and pyruvic acids accumulate, leading to local acidosis.
- pH shift: in healthy tissue, pH is about 7.1, whereas in a purulent wound it drops to 6.0–6.5. Acidosis stimulates exudation, macrophage migration, and phagocytosis.
- Electrolyte imbalance: destroyed cells release potassium abundantly (its concentration increases 50–100 fold), which disrupts the potassium-calcium balance.
- Protein metabolism: catabolism initially predominates (protein breakdown due to necrosis and enzyme activity), followed by anabolism (collagen synthesis involving proline).
Phases of the wound healing process
Healing occurs in three main phases that smoothly transition into one another:
- Inflammatory phase (alteration, exudation, necrolysis). Begins immediately after trauma. Vasospasm occurs, followed by paralytic vasodilation. Neutrophils, which form a demarcation wall, and macrophages actively migrate into the wound. The main task is the lysis of necrotic tissue and clearance of microbes.
- Proliferative phase. Starts on days 2–3. Characterized by angiogenesis (growth of new capillaries) and fibroblast proliferation. As a result, a lush, bright red granulation tissue is formed. It performs reparative, barrier, and cleansing functions.
- Healing phase (scarring and epithelialization). Develops in 2–4 weeks. Vessels are obliterated, and the number of cellular elements decreases. Fibroblasts actively synthesize collagen and elastic fibers. Concurrently, the basal epithelium, lacking skin appendages, creeps from the edges of the wound.
Types of wound healing
Depending on the conditions in the wound, healing follows one of several scenarios:
- Primary intention: the optimal option with a minimal healing time. Requires tight approximation of the edges (distance of 50–500 µm) and secure fixation.
- Secondary intention: a longer pathway. The wound fills with granulation tissue, which is gradually replaced by a scar.
The course of the process can be favorable (edema subsides, necrotic tissue sloughs off) or unfavorable (intoxication increases, purulent discharge grows, necrosis progresses).
Complications
Depending on the time of onset, early and late complications are distinguished:
- Early: traumatic shock, acute blood loss, and anemia.
- Late: suppuration, secondary hemorrhage, sepsis, tetanus, and gas gangrene.
Briefly: answers to topical questions
What types of wound healing are distinguished?
There are three main and one additional type of wound healing.
- Healing by primary intention (sanatio per primam intentionem) occurs when the edges and walls of the wound are in contact, inflammation is mild, and a thin linear scar is formed.
- Healing by secondary intention (sanatio per secundum intentionem) occurs when the edges are separated by more than 10 mm, characterized by pronounced purulent inflammation, filling of the defect with granulations, and a massive scar.
- Healing under a scab is typical for small superficial injuries (abrasions); the defect is covered by dried exudate.
- Mixed type of healing — part of the wound heals by primary and part by secondary intention.
What conditions are necessary for wound healing by primary intention?
For wound healing by primary intention, close approximation of the edges and walls of the wound defect is necessary. The following mandatory conditions are distinguished:
- Tight adaptation of the wound edges and walls with a minimal distance between them.
- A small amount of microbial flora in the wound.
- Low virulence of microorganisms.
- A small volume of damaged and non-viable tissues.
Such conditions are ensured by the nature of the trauma itself (e.g., in an incised wound with even edges) or achieved artificially through surgical approximation of the edges (placement of primary sutures).
What major growth factors and mediators regulate wound healing?
Wound healing is regulated by a complex of biologically active substances, cytokines, and growth factors. The main mediators and factors include:
- Platelet-derived growth factor (PDGF) attracts fibroblasts and endothelial cells to the defect area.
- Vascular endothelial growth factor (VEGF) and angiogenic factor participate in endothelial cell proliferation and angiogenesis.
- Fibroblast growth factor (FGF) belongs to growth and angiogenic factors produced by macrophages.
- Epidermal growth factor is used to accelerate wound healing.
- Biologically active substances — histamine, serotonin, kinins, prostaglandins, bradykinin, and heparin sodium — participate in inflammation and regulate vascular permeability.
- ATP and ADP derivatives stimulate the migration and phagocytic activity of leukocytes and activate regeneration.
Class and exam questions
How to distinguish healthy granulations from pathological ones?
Healthy granulations are dense, granular, lush, and bright red. Pathological ones appear pale, dull, watery, and bleed easily at the slightest touch.
Why does a keloid scar form?
A keloid forms when the growth of granulation tissue outpaces the process of wound epithelialization, leading to excessive scar overgrowth above the skin level.
What else to study on this topic
- Classification of wounds by the nature of the projectile injury
- The role of biologically active substances (kinins, prostaglandins) in inflammation
- Intracellular and extracellular proteolysis in the wound
- Cellular composition and layered structure of granulation tissue
- Mechanisms of angiogenesis at the wound base
Master the entire topic in the "General Surgery" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the "Wound healing process" and 3,335 other pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 70 video lessons on the subject
Other topics in "CHAPTER 10. GENERAL ISSUES IN TRAUMATOLOGY"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.