A 32-year-old man sustains a laceration to his forearm during a workplace injury. Histological examination of the wound at day 5 post-injury shows predominant fibroblast activity and collagen deposition. Which is the most common type of collagen deposited during this phase of wound healing?

Explanation

## Collagen Deposition in Wound Healing ### Timeline of Collagen Synthesis **Key Point:** Type III collagen is the predominant collagen type deposited during the early proliferative phase (days 3–21 post-injury), while Type I collagen becomes dominant in the remodeling phase (weeks 3–12 months). ### Collagen Types in Wound Healing | Collagen Type | Timeline | Characteristics | Proportion at Day 5 | | --- | --- | --- | --- | | **Type III** | Days 3–21 (early proliferative) | Thin fibrils, less tensile strength, more soluble | **70–80% of new collagen** | | **Type I** | Weeks 3–12 months (remodeling) | Thick fibrils, high tensile strength, cross-linked | Increases gradually; replaces Type III | | **Type II** | Cartilage matrix | Not involved in skin wound healing | Absent | | **Type IV** | Basement membrane | Structural, not involved in scar formation | Minimal | ### Clinical Pearl **High-Yield:** At day 5 post-injury, the wound is in the **proliferative phase**. Fibroblasts are actively synthesizing collagen, and Type III collagen predominates because it is synthesized first and more rapidly. The ratio of Type III:Type I gradually shifts toward Type I over weeks to months during the remodeling phase, which is why scars become stronger and less extensible with time. ### Mechanism 1. Fibroblasts migrate into the wound bed (day 3 onwards) 2. Type III collagen is synthesized first (rapid, thin fibrils) 3. Type I collagen synthesis increases gradually 4. Cross-linking and maturation occur over months 5. Final scar contains ~80% Type I and ~20% Type III collagen **Mnemonic:** **"3 comes before 1"** — Type **III** collagen is deposited **before** Type **I** collagen in wound healing chronology.