Repair

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Repair

• DR .HALA Badawi
• Lecturer of pathology

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Repair

• Definition
• Repair is the replacement of damaged tissue by
  new healthy one
• Types of Repair
• I- Regeneration
• II- Healing by fibrosis

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Cell Cycle and Proliferative Potential

• The cells of the body are divided into three
  groups on the basis of their proliferative
  capacity and their relationship to the cell
  cycle.
• 1- Continuously dividing cells (also called
  labile cells) e.g. skin, urinary GIT mucosa and
  blood lymphoid tissue
• 2- Quiescent (or stable) cells e.g. liver,
  kidney, pancrease fibroblasts
• 3- Nondividing (permanent) cells e.g. nerve
  cells and cardiac striated muscles

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CONTROL OF NORMAL CELL GROWTH

• Cell replication is controlled largely by
  chemical factors (growth factors) in the
  microenvironment, which either stimulate or
  inhibit cell proliferation.

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Regeneration

• Definition
• Regeneration is the replacement of damaged cells
  by new cells of the same kind
• Examples of Regeneration
• Regeneration of skin
• Regeneration of liver cells
• Repair of bone fracture
• Healing of peripheral nerve

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Regeneration of Liver Cells 1- When the injury is
limited and the fibrous framework is preserved,
complete regeneration occurs 2- when the damage
is severe and the framework is destroyed,
regenerating nodules and fibrosis resulting in
cirrhosis
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Healing of bone fracture
Phases of fracture healing There are three major
phases of fracture healing 1. Reactive Phase
i. Fracture and inflammatory phase ii.
Granulation tissue formation 2. Reparative
Phase iii. Callus formation iv. Lamellar bone
deposition 3. Remodeling Phase v. Remodeling
to original bone contour
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2
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Repair of Peripheral Nerve

• Nerve injury and repair
• Normal axon and target organ (striated muscle).
• Following nerve injury the distal part of the
  axon disintegrates and the myelin sheath breaks
  up. The nerve cell nucleus becomes eccentric and
  Nissl granules decreased.
• New axonal tendrills grow into the mass of
  proliferating Schwann cells. One of the tendrill
  will find its way into the old endoneurial tube
• the axon will slowly regenerate

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Healing by fibrosis

• Definition
• Replacement of damaged tissue by fibrous
  tissue through formation of granulation tissue.
• Granulation tissue
• Consists of new capillary loops and
  proliferating fibroblasts

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Granulation tissue 1- Red granular surface 2-
Moist 3- Bleeds easily 4- Insensitive
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Healing of Wounds

• I- Primary Union of Wounds
• (Healing by First Intention)
• Clean incised wound with minimal tissue
  destruction
• II- Secondary Union of Wounds
• (Healing by Second Intention)
• Gaping septic wounds with marked tissue
  destruction

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Healing of Wounds

• I- Primary Union of Wounds
• Is the healing of a clean, uninfected surgical
  incision approximated by surgical sutures.
• The narrow incisional space immediately fills
  with clotted blood and the surface is covered
  by scab.
• Within 24 hours, neutrophils infiltrate the clot.
  
• Within 24 to 48 hours the epidermis grow along
  the cut margins of the dermis producing a
  continuous thin epithelial layer beneath the
  surface scab.

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Healing of Wounds

• I- Primary Union of Wounds (continue)
• By day 3, the neutrophils have been largely
  replaced by macrophages and granulation tissue
  started to appear.
• By day 5, the incisional space is filled with
  granulation tissue.
• The epidermis recovers its normal thickness by
• day 5-7
• During the second week, there is continuous
  maturation of granulation tissue to fibrous
  tissue
• By the end of the first month, complete
  deposition of collagen with formation of thin
  incisional scar

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6 hours
24 hours
2 days
1 week
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Wound healing ( 1ry union)
Wound healing ( 1ry union)
Healed wound
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Healing of Wounds

• II- Secondary Union of Wounds
• (Healing by Second Intention)
• When there is extensive loss of tissue and
  surface wounds that create large defects, the
  reparative process is more complicated.

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Healing of Wounds

• Secondary healing differs from primary healing in
  several respects
• Large tissue defects, have more fibrin and more
  necrotic debris with intense inflammatory
  reaction.
• Much larger amounts of granulation tissue formed.
  
• The most clear difference between primary and
  secondary healing is the phenomenon of wound
  contraction, which occurs in large surface
  wounds.

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first intention healing
second intention healing
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Wound Strength

• When sutures are removed, usually at the end of
  the first week, wound strength is approximately
  10 of the strength of unwounded skin.
• But it increases rapidly over the next 4 weeks.
• This rate of increase then slows at approximately
  the third month after the original incision and
  then reaches a plateau at about 70 to 80 of the
  tensile strength of unwounded skin, which may
  persist for life.
• The recovery of tensile strength results from
  increased collagen synthesis exceeding collagen
  degradation during the first 2 months and from
  structural modifications of collagen fibers.

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Factors Affecting Wound Healing

• Systemic factors include the following
• Nutrition has intense effects on wound healing.
  Protein deficiency, for example, and vitamin C
  deficiency inhibit collagen synthesis and retard
  healing.
• Metabolic status can change wound healing.
  Diabetes mellitus, for example, is associated
  with delayed healing.
• Blood supply, Inadequate blood supply usually
  caused by arteriosclerosis or venous
  abnormalities that retard venous drainage also
  impair healing.
• Hormones, such as glucocorticoids, have
  anti-inflammatory effects and inhibit collagen
  synthesis

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Factors Affecting Wound Healing

• Local factors that influcence healing include
  the following
• Infection is the single most important cause of
  delay in healing.
• Mechanical factors, as early motion of wounds,
  can delay healing.
• Foreign bodies, such as unnecessary sutures or
  fragments of steel, glass, or even bone,
  constitute impediments to healing.
• Size, location, and type of wound influence
  healing. Wounds in richly vascularized areas,
  such as the face, heal faster than those in
  poorly vascularized ones, such as the foot. Small
  injuries and surgical wounds heal faster than
  larger ones caused by blunt trauma.

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Complications of Wounds Healing

• Wound rupture and ulceration
• Rupture of a wound is most common after
  abdominal surgery. Ulceration occur due to
  inadequate vascularization.

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Complications of Wounds Healing

• 2- Keloid
• The accumulation of excessive amounts of
  collagen may give rise to a raised tumorous scar
  known as a keloid, which is more common in blacks.

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Complications of Wounds Healing

• 3- Exuberant granulation
• formation of excessive amounts of granulation
  tissue.

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Complications of Wounds Healing

• 4- Desmoids tumour
• proliferations of fibroblasts and collagen
  forming a mass that recur after excision.

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Complications of Wounds Healing

• 5- Contractur exaggeration of wound contraction,
  results in deformities of the wound and the
  surrounding tissues.
• Contractures are commonly seen after serious
  burns and can compromise the movement of joints.

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TISSUE REPAIR SUMMARY

• Not all injuries result in permanent damage some
  are resolved with almost perfect return of normal
  structure and function (resolution).
• Resolution occurs with minimal or no tissue
  damage.
• More often, there is some degree of scarring
• Scar is usually good (provides a resilient patch)
  but occasionally bad (can cause permanent
  dysfunction)

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