A 39-year-old man comes to the physician for a follow-up examination. He was treated for a urinary tract infection with trimethoprim-sulfamethoxazole 2 months ago. He is paraplegic as a result of a burst lumbar fracture that occurred after a fall 5 years ago. He has hypertension and type 2 diabetes mellitus. Current medications include enalapril and metformin. He performs clean intermittent catheterization daily. He has smoked one pack of cigarettes daily for 19 years. His temperature is 37.1°C (98.8°F), pulse is 95/min, respirations are 14/min, and blood pressure is 120/80 mm Hg. He appears malnourished. Examination shows palpable pedal pulse. Multiple dilated tortuous veins are present over both lower extremities. There is a 2-cm wound surrounded by partial-thickness loss of skin and a pink wound bed over the right calcaneum. Neurologic examination shows paraparesis. His hemoglobin A1c is 6.5%, and fingerstick blood glucose concentration is 134 mg/dL. Which of the following is most likely to have prevented this patient's wound?

Broad-spectrum antibiotic therapy

A 45-year-old man comes to his primary care provider for a routine visit. The patient mentions that while he was cooking 5 days ago, he accidentally cut himself with a meat cleaver and lost the skin at the tip of his finger. After applying pressure and ice, the bleeding stopped and he did not seek treatment. The patient is otherwise healthy and does not take any daily medications. The patient’s temperature is 98.2°F (36.8°C), blood pressure is 114/72 mmHg, pulse is 60/min, and respirations are 12/min. On exam, the patient demonstrates a 0.5 x 0.3 cm wound on the tip of his left third finger. No bone is involved, and the wound is red, soft, and painless. There are no signs of infection. Which of the following can be expected on histopathological examination of the wounded area?

Deposition of type III collagen

Epithelial cell migration from the wound borders

Neutrophil migration into the wound

A 48-year-old man is brought to the emergency department with a stab wound to his chest. The wound is treated in the emergency room. Three months later he develops a firm 4 x 3 cm nodular mass with intact epithelium over the site of the chest wound. On local examination, the scar is firm, non-tender, and there is no erythema. The mass is excised and microscopic examination reveals fibroblasts with plentiful collagen. Which of the following processes is most likely related to the series of events mentioned above?

Foreign body response from suturing

Poor wound healing from diabetes mellitus

A 33-year-old Caucasian female presents to her primary care provider for skin problems and difficulty breathing. She has not sought medical care in over 10 years due to anxiety around physicians. However, she has experienced gradual onset of diffuse pruritus, skin induration, and limited finger mobility over the past 5 years that has negatively impacted her work as an accountant. More recently, she has developed exertional shortness of breath and is concerned that it may impact her ability to care for her 3-year-old son. She reports no prior medical conditions and takes fish oil. She smokes 1 pack of cigarettes per day and drinks socially. Her temperature is 98.6°F (37°C), blood pressure is 145/85 mmHg, pulse is 85/min, and respirations are 22/min. On exam, she appears anxious with minimally increased work of breathing. Dry rales are heard at her lung bases bilaterally. Her fingers appear shiny and do not have wrinkles on the skin folds. A normal S1 and S2 are heard on cardiac auscultation. This patient’s lung disease is caused by increased secretion of which of the following substances within the lungs?

Transforming growth factor beta

Wound healing and repair for USMLE Step 2 CK: High-Yield Pathology Lessons

Tissue Repair - Regeneration vs. Scarface

Wound Healing Process: Inflammation, Granulation, Scarring

Regeneration: Perfect restoration of tissue architecture and function.
- Occurs in labile (skin, gut) & stable tissues (liver).
- Requires an intact extracellular matrix (ECM) scaffold.
Repair (Scarring): Replacement with a fibrous scar.
- Occurs in permanent tissues (heart, neurons) or with severe ECM damage.
- Provides stability but with functional loss.

⭐ The extracellular matrix (ECM) is the critical determinant. If the ECM scaffold is damaged, healing results in a scar, regardless of the tissue's regenerative capacity.

Healing Phases - From Mess to Success

1. Inflammatory Phase (0-3 days)
- Hemostasis: Platelet plug & fibrin clot formation.
- Inflammation: Neutrophils arrive first (peak ~24h), followed by macrophages (peak ~48-72h), which are crucial for cleanup and transition to the next phase.
2. Proliferative Phase (Day 3-Weeks)
- Granulation tissue forms: Fibroblasts deposit Type III collagen, new capillaries grow (angiogenesis), and myofibroblasts cause wound contraction.
- Epithelialization covers the wound.
3. Remodeling Phase (Week 1-Months/Years)
- Type III collagen is replaced by stronger Type I collagen (Collagenases require Zinc).
- Tensile strength increases over time.

⭐ By 3 months, wound strength is approximately 70-80% of unwounded skin, a common point of failure in post-op recovery.

Mammalian wound healing phases: cells, vessels, collagen

Healing Intention - Stitches & Ditches

Primary vs. Secondary Intention Wound Healing

Primary Intention (Stitches)
- Mechanism: Clean, surgical wound edges approximated by sutures.
- Process: Minimal tissue loss, clot, and inflammation. Less granulation tissue forms.
- Result: Rapid healing with a fine, linear scar.
Secondary Intention (Ditches)
- Mechanism: Large, open wounds with significant tissue loss (e.g., ulcers, abscesses).
- Process: Abundant granulation tissue fills the defect, followed by wound contraction.
- Result: Slower healing, larger scar.

⭐ Myofibroblasts are the key cells responsible for wound contraction in secondary intention, significantly reducing the size of the defect over time.

Healing Factors - What Slows the Show

Systemic: Malnutrition (↓ Vit C, copper, zinc), Diabetes Mellitus (impaired leukocyte function, ↓ perfusion), corticosteroids (anti-inflammatory effects), smoking (vasoconstriction), advanced age.
Local: Infection, ischemia/hypoxia (↓ ATP for collagen synthesis), foreign body, excessive movement, poor tissue apposition.

⭐ Infection is the single most common cause of delayed wound healing, with Staphylococcus aureus being a frequent culprit.

Healing Complications - Scars & Problems

Hypertrophic Scar: Excess Type III collagen; raised but confined to original wound boundaries. Collagen fibers are parallel.
Keloid: Disorganized, thick Type I & III collagen bundles extending beyond wound borders. High recurrence rate. Common in individuals of African descent.
Contracture: Exaggerated wound contraction via myofibroblasts, causing deformity (e.g., after burns) and limiting mobility.
Dehiscence: Premature bursting open of a previously closed wound.

⭐ Keloids are characterized by haphazardly arranged, thick bundles of Type I and III collagen, unlike the parallel fibers seen in hypertrophic scars.

High‑Yield Points - ⚡ Biggest Takeaways

Healing phases: Inflammatory (neutrophils, macrophages), Proliferative (fibroblasts, granulation tissue), and Remodeling (collagen maturation).

Secondary intention involves significant granulation, contraction by myofibroblasts, and results in a larger scar.

The critical collagen transition is from Type III collagen (weak) to Type I collagen (strong), a process dependent on Vitamin C.

TGF-β is the key cytokine driving fibrosis; VEGF and FGF are critical for angiogenesis.

Keloids consist of excessive collagen extending beyond the original wound borders, unlike hypertrophic scars.

Wound dehiscence is strongly associated with infection, malnutrition, and obesity.

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Wound healing and repair