Chapter 2 Innate and Adaptive Immunity: From Cell Defense to Tissue Repair
Section 12: Healing and Tissue Repair
Zoë Soon
Three Outcomes Following Acute Inflammation
| Resolution | Damaged cells recover without dying. Full function is restored. |
| Regeneration | Lost cells replaced by the same cell type via stem cell mitosis.
Many epithelial cells, connective tissue cells, and liver cells are highly regenerative. |
| Replacement (Fibrosis) | In non-regenerative tissues (cardiac muscle, skeletal muscle, kidney cells, brain and spinal cord neurons, most cartilage) or large wounds, collagen and fibroblasts replace lost tissue forming scar tissue.
This process – fibrosis – involves permanent loss of functional tissue. |
During healing: capillaries become less permeable, blood vessel diameter normalizes, WBCs inactivate, fibrin is dissolved, excess interstitial fluid is absorbed by lymph vessels, and the signs of inflammation – redness, warmth, swelling, pain – all diminish.
Complications of Tissue Damage and Inflammation
| Chronic inflammation | If the irritant source is not removed, WBC activity perpetuates tissue destruction cycles and progressive fibrosis. |
| Infection | Wounds exposed to the environment may be colonized by opportunistic microbes – even normal flora – causing further damage. |
| Deep ulcers | Damage to gastric mucosa allows stomach acid to erode underlying tissue, causing severe, prolonged inflammation, bleeding, necrosis, and fibrosis. |
| Skeletal muscle spasms | Protective response to pain during sprains and strains.
In bone fractures, spasms can shear tissue by forcing bone ends to move. Note: Temporary muscle spasms (e.g. charley horse) during excessive exercise are different in that the cause is thought to be not enough blood flow, cellular dehydration, and/or electrolyte depletion. |
| Peripheral and Central nerve damage | Periphery nerve damage can result in permanent or temporary loss of sensation (paresthesia), muscle weakness, or paralysis. Peripheral nerves may partially recover.
Brain/spinal cord neuronal loss is permanent; brain plasticity (remodelling) can sometimes occur to allow for partial recovery of some lost functions. |
| Obstruction | Esophageal swelling impairs swallowing; bronchiole/bronchi swelling impairs breathing and gas exchange. |
| Increased Intracranial Pressure (ICP) | Swelling in the brain or cranial meninges can pinch off capillaries, reducing blood flow – potentially fatal. |
| Myositis Ossificans | Calcification within injured muscles (most commonly arm or thigh).
Risk factors include deep contusions from contact sports. Prevention: prompt RICE therapy. |
Chronic Inflammation
Chronic inflammation follows acute inflammation when the irritant is not fully removed – e.g., ongoing infection, smoking, pollutants, cancer, diabetes, or autoimmune diseases such as Rheumatoid Arthritis or Systemic Lupus Erythematosus (SLE). Compared to acute inflammation, chronic inflammation features:
- Less swelling and exudate
- More angiogenesis (new capillary formation)
- More lymphocytes, macrophages, and fibroblasts
- Continued tissue destruction
- Increased collagen → fibrous scar tissue (fibrosis)
- Possible granuloma formation (small masses of cells with a necrotic center covered by connective tissue) – seen in rheumatoid arthritis, osteoarthritis, around foreign objects, or at sites of chronic infection such as tuberculosis.
