Inflammation and repair
Introduced| English | Meaning |
|---|---|
| acute inflammation | acute inflammation |
| chronic inflammation | chronic inflammation |
| granuloma | A tight cluster of activated macrophages, often with giant cells, that walls off something the body cannot remove. |
| granulation tissue | granulation tissue |
Red and hot within the hour, a scar in three months
- A cut finger is red, warm, swollen and sore within the hour. Three months later it has a pale scar that is still weaker than the skin around it.
- Inflammation and repair run on a schedule, and the cells present tell you where on the schedule a tissue is.
Acute inflammation
- Acute inflammation 急性炎症 lasts minutes to days. Vessels widen and leak, fluid and protein form an exudate, and neutrophils pour in.
- The five classic signs: redness, heat, swelling, pain and loss of function.
Which cell dominates acute inflammation?
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Neutrophils arrive first and in the greatest numbers.
Chronic inflammation
- Chronic inflammation 慢性炎症 is defined by its cells: macrophages, lymphocytes and plasma cells, with tissue damage and repair going on together.
- It usually ends in scarring.
Granulomas
- A granuloma 肉芽肿 is a tight cluster of activated macrophages, often with giant cells, that walls off something the body cannot remove.
- Caseating granulomas (with central necrosis) suggest tuberculosis; non-caseating ones suggest sarcoidosis.
Match each finding to what it suggests.
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The cells and the pattern tell you the kind and the cause.
Granulation tissue is a kind of granuloma.
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Granulation tissue is repair tissue of fibroblasts and new vessels; a granuloma is a cluster of macrophages.
The repair schedule
- A clot forms within hours; neutrophils, then macrophages, clean up over days 1–3; granulation tissue 肉芽组织 (fibroblasts, new vessels and type III collagen) fills the gap on days 3–7.
- Over months the scar remodels: type I collagen replaces type III.
Put the phases of wound healing in order.
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Each phase has its own cells and its own clock.
How strong is the scar?
- A wound has about 10% of normal strength at one week, gains fast over the next month and levels off at about 70–80% from three months. It never reaches 100%.
- A clean wound with edges held together heals by first intention, quickly; an open wound fills from the bottom by second intention, slowly, with more scar.
Unwounded skin withstands 50 units of force. A scar at 6 months has 75% of that strength. How many units does it withstand?
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50 × 0.75 = 37.5; the scar never gets back to 50.
Why must a wound be protected by sutures in the first week?
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Collagen has barely started to form, so stitches hold what the scar cannot.
Worked example: dating a wound
- (Fictional teaching slide) Neutrophils fill the wound: day 1–3. Fibroblasts, new capillaries and pale type III collagen: day 3–7.
- By two weeks the macrophages are fewer and collagen bridges the gap. Each field under the microscope carries a date.
A wound shows fibroblasts, new capillaries and type III collagen. About how old is it?
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That is granulation tissue, the proliferation phase.
Worked example: the granuloma fork
- (Fictional) A lung nodule is biopsied. Granulomas with cheese-like centres: look for mycobacteria (tuberculosis).
- Granulomas without necrosis and no organism found: think sarcoidosis. One finding, necrosis or not, splits the investigation.
Three common slips
- Calling granulation tissue a granuloma. Granulation tissue is repair (vessels and collagen); a granuloma is a cluster of macrophages.
- Defining chronic inflammation by time alone. It is defined by its cells.
- Expecting a scar to regain full strength. It peaks at about 70–80%.
Recap
- Acute: neutrophils, exudate, five classic signs. Chronic: macrophages, lymphocytes, plasma cells, scarring.
- Granulomas: caseating (tuberculosis) or non-caseating (sarcoidosis).
- Clot (hours) → clean-up (days 1–3) → granulation tissue (days 3–7) → remodelling (months), reaching 70–80% strength.