Page 80 - Concise Pathology for Exam Preparation ( PDFDrive )

3 Healing and Repair 65

Formation of a haematoma due to bleeding from torn blood vessels

Loose meshwork formed by blood fills the fracture gap

Local inflammatory response

Exudation of fibrin, polymorphs and macrophages at the site of fracture

Ingrowth of granulation tissue (begins with neovascularization)

The degranulated platelets and inflammatory cells secrete mediators that activate osteoprogenitor cells in the
periosteum, medullary cavity and surrounding soft tissue

Soft tissue callus or procallus formation (end of the first week)

Osteoprogenitor cells lay down collagen as well as osteoid matrix in granulation tissue

• Calcification of osteoid (woven bone callus)
• Deposition of fibrocartilage and hyaline cartilage

Woven bone is cleared away by osteoclasts and the calcified cartilage disintegrates; in its place lamellar bone
with haversian system is laid down

Remodelling
(realignment and mechanical chopping of bone; development of medullary canal)

Compact bone formation
FLOWCHART 3.6. Steps in callus formation.

2. Healing of nervous tissue:
(a) Central nervous system: Nerve cells of brain, spinal cord and ganglia once de-
stroyed are not replaced. Neuroglial cells, however, may show proliferation called
gliosis.
(b) Peripheral nervous system: Proliferation of Schwann cells and fibrils from distal
ends is seen in response to injury.
3. Healing of muscle:
(a) Skeletal muscle:
(i) If the muscle sheath is intact, sarcolemmal tubes appear along endomysium
and restore muscle fibres, eg, Zenker degeneration of the muscle in typhoid.
(ii) If the muscle sheath is damaged, a disorganized multinucleated mass and scar
comprised of fibrovascular tissue form, eg, Volkmann ischaemic contracture.
(b) Cardiac muscle: Replaced by the permanent scar tissue, eg, cardiac muscle is
replaced by fibrous tissue in myocardial infarction
4. Healing of solid epithelial organs:
In parenchymal cell damage with intact basement membrane, regeneration and resto-
ration are possible; however, gross tissue damage to these organs lead to healing by
fibrous scarring, eg, chronic pyelonephritis.

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