This document summarizes different types of tissue repair and regeneration processes in the body. It discusses regeneration of epithelial tissues like skin and mucous membranes. It provides a detailed overview of the 7 stages of bone fracture healing. It also describes the mechanisms of peripheral nerve regeneration and central nervous system repair, noting that nerve cells in the CNS cannot regenerate. Defects in bone healing and traumatic neuromas are also mentioned.

1. REPAIR
By
Shatha al sulh

2. Repair by regeneration
• Replacement of the damaged tissue by tissues of the same
type.
• Cells capable of regeneration: labile & stable ( not the
permanent ).
• Examples of regeneration::
of epidermis:
• Abrasion: superficial injury complete
regeneration.
• Skin wound: injury of epid. & dermis
epidermal regeneration but dermal fibrosis.
Of mucous membranes of GIT & UT.

3. Healing of bone fracture
• Healing of bone (≥ 4w) may be so perfect
that the fracture site may not be identified.
• Michanism:
• Stage 1: hematoma.
• Stage 2: inflammatory exudate (traumatic
inflammation).
• Stage 3: demolition (phagocytosis by
macrophages & osteoclast with gradual
removal of damaged bone fragments, blood
& inflammatory cells & release of GF).
• Stage 4: granulation tissue formation
(procallus ): consists of capillary loops &
msenchymal cells.
Fracture bone hematoma

4. Healing of bone fracture (cont.)
• Stage 5:woven bone & cartilage (provisional callus):
• Chondroblast cartilage islands.
• Osteoblast osteoid tissue (bone matrix+collagen) lacking calcification.
• Gradual loss of capillaries.
• Gradual calcification of osteoid tissue (by ALP) woven bone.
• Stage 6:formation of lamellar bone (permanent callus): cartilage desentigration
& woven bone replacement by lamellar bone ( osteoclasts) Haversian
system formation.
• Stage 7:remodeling of callus:
• Removal of internal & external callus (by osteoclasts).
• Adjustment of intermediate callus (size, strength & lamellar property) by
osteoblasts & osteoclasts , in response to mechanical stress along lines of wt.
bearing.
• BM regenerates inside the medullary canal.

5. Woven boneLamellar bone

6. Causes of defective bone healing
(nonunion,weak union or pseudoarthrosis)
• Local factors:
• Inadequate immobilization.
• Malalignment.
• Pathological fracture.
• Soft tissue interposition.
• Ischemia.
• Infection.
• General factors:
• Old age.
• Nutritional deficiencies.
• Glucocorticoid therapy.
• DM.

7. Healing of damage to nervous system:
Injury of perepheral nerve:
• regenerated as the nerve cells are preserved.
• Michanism of regeneration of PN cut:
• Nerve injury leads to :
• Axonal degeneration of nerve cells (swollen, eccentric neuclei & loss Nissel
granules)
• Wallarian degeneration: disintegration of myelin & axis cylinder (proximal &
distal).
• Schwann cells:
• Resist injury, phagocytosis of Wallarian degeneration products (with
macrophages), proliferate (distal & proximal) integrated neurilemmal
tube.

8. Healing of damage to nervous system (
cont.):
• Growth of axis cylinders (secreated by alive nerve cells)inside
integrated neurilemmal tube (1mm/d),
• Myelin sheath formation around the growing axons (final stage)
Traumatic neuroma:
• Complication of nerve healing.
• Painful mass.
• If the 2 ends of the nerve are not opposite each other or if the nerve is severed
(absent distal segment).
• Proliferating Schwann cells & neurofilaments mix.

10. Healing of damage to nervous system (
cont.):
Damage of CNS:
• Damage of nerve cells (in brain & spinal cord).
• Can never be regenerated (nerve cells can not divide).
• Repair:
• Phagocytosis of dead tissue (macrophages & microglia
cells).
• Lay down special type of CT by astrocytes (gliosis).