Transcript Repair - BMC Dentists 2011

Repair
DR .HALA Badawi
Lecturer of pathology
Repair
• Definition:
Repair is the replacement of damaged tissue by
new healthy one
• Types of Repair
I- Regeneration
II- Healing by fibrosis
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
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.
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
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
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
1
2
2. Reparative Phase
iii. Callus formation
iv. Lamellar bone deposition
3. Remodeling Phase
v. Remodeling to original bone
contour
3
Repair of Peripheral Nerve
Nerve injury and repair
(a)Normal axon and target organ
(striated muscle).
(b)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.
(c)New axonal tendrills grow into the
mass of proliferating Schwann cells.
One of the tendrill will find its way
into the old endoneurial tube
(d)the axon will slowly regenerate
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
Granulation tissue
1- Red granular surface
2- Moist
3- Bleeds easily
4- Insensitive
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
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.
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
24 hours
6 hours
2 days
1 week
Wound healing
Wound healing
( 1ry union)
( 1ry union)
Healed wound
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.
Healing of Wounds
Secondary healing differs from primary healing in
several respects:
1. Large tissue defects, have more fibrin and more
necrotic debris with intense inflammatory reaction.
2. Much larger amounts of granulation tissue formed.
3. The most clear difference between primary and
secondary healing is the phenomenon of wound
contraction, which occurs in large surface wounds.
first intention healing
second intention healing
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.
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
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.
Complications of Wounds Healing
1. Wound rupture and
ulceration:
Rupture of a wound is most
common after abdominal
surgery. Ulceration occur
due to inadequate
vascularization.
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.
Complications of Wounds Healing
3- Exuberant granulation:
formation of excessive amounts
of granulation tissue.
Complications of Wounds Healing
4- Desmoids tumour:
proliferations of fibroblasts
and collagen forming a mass
that recur after excision.
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.
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)