1.
Healing and repair 3

2.
Bone Healing:
In three primary phases o: Reactive, Reparative, and Remodeling
phase. any one of these phases has stages or steps to follow.

3.
1. Reactive phase:
- Step 1: Hematoma is (localized blood collection) that formed
within the fracture site in the first few hours and days.
- Step 2: Inflammatory cells infiltrate with in the fractured
bone, with recruiting of neutrophil then macrophages
- Step3: granulation tissue (important in healing). New
Vascular formation for nutrition delivery, fibroblast
accumulation will specialize cells to form a bridge of tough
connective tissue. - This stage can last 2 – 4 weeks after a
fracture, and it overlaps with the next stage

4.
2. Reparative phase:
- This is the phase where the fracture gets completely healed.
the edges of the bone become joined together and stabilized.
- Callus: special cells in the body that are capable of changing
into bone cells are activated or fired up to do so, and they
start laying down new bone tissue; this tissue, is a soft tissue
called callus.
- hardening of callus begins at each end of the fracture and
sweeps toward the center. the new blood vessels for the new
growth are also getting mature. This stage can last 1 – 2
months after a fracture

5.
3. Remodeling phase: This is the phase where the bone should be
restored to its original shape, structure, and mechanical
strength; remodeling of the bone occurs slowly over months to
years.

6.
Neurons Healing: neuron cell + supporting cells
Neurons:
(Nerve cells) are specialized cells that can receive and conduct
electrical impulses; all of the neurons have the same basic structure:
1- Dendrite: extends from the cell body (dendron - greek for tree).
These are the part at which nerve impulses are received.
2- The cell body: Most of the bodies are found in the brain and spinal
cord, or in the ganglia (which lie just outside the spinal cord).
3- The axon: a single nerve fiber, which transmits impulses to the
distal end. Axons can be very long - around 1 meter, and vary in
diameter from 0.2 to 20 µm

7.
Supporting cells in the central nervous system.
four types of supporting cells.
1. Oligodendrocytes: Myelin is formed by oligodendrocytes in the CNS, and
by Schwann cells in the PNS). axons are insulated by a myelin sheath, which
increases the rate at which an axon can conduct an action potential.
2. Microglia: They have a role in immune defense and become phagocytic in
response to infections or tissue damage.
3. Astrocyte: These are supporting cells, also involved in the metabolic
exchange between neurons and blood, and responsible for blood-brain brier
4. Ependymal cells: line the ventricles and spinal canal producing CSF. They
have cilia on their luminal surface.
Peripheral nervous system: In the peripheral nervous system, there
are two types of supporting cell, the Schwann and satellite cells

8.
Healing process in neuronal tissue:
A- Injury to the cell body: usually resulted in the death of the neuron,
(Permanent cell)
B- Injury to an axon in the peripheral nervous system:.
if injury cuts an axon from its cell body:
• the distal portion of the axon and disappears within a few weeks by the
action of Macrophages
• The proximal end of the injured axon develops sprouts, by the action of
nerve growth factors. one of these sprouts may grow into a tube formed by the
remaining basement membrane and Schwan cell, Schwann cells proliferate
along the length of the degenerating portion and form new myelin around the
growing axon.

9.
NB
• Growth of a regenerating axon is very slow about 3 millimeters per day,
• Nerve growth factors, secreted by glial cells, help to direct the growing axon.
• Complication: the regenerating axon may still end up in the wrong place, so
full function often does not return.
C- Injury of an axon of a neuron within the central nervous
system:
• If an axon is cut from its cell body:
- the distal portion of the axon will not degenerate.
- the proximal end begins to grow, it will find no tube to guide it, therefore,
regeneration is unlikely.
• the myelin-producing oligodendrocytes in the central nervous system cant
proliferate following an injury.

10.
• Healing in CNS by (Glial scar):
• Gliosis formation is a reactive cellular process involving mainly
astrocytes and microglia cells.
Astrogliosis
• As with scarring in other organs, the glial scar is the mechanism that
begins the healing process.
• astrocytes are the main cellular component of the glial scar.
• after injury: astrocytes undergo morphological changes: extend
their processes to form a dense web of extensions that fills the
empty space generated by the dead neuronal cells (a process called
astrogliosis).
Microgliosis
- Microglia are the second most prominent cell present within the
glial scar. They are the analog of macrophages. Microglia rapidly
activate near the injury and secrete several cytokines.