Developmental biology

1. HISTOLOGICAL
PROCESSES DURING
REGENERATION
Submitted by
Ajay Dominic V
Roll no:251

2.  Regeneration is a series of histological
transformation.
 Needham [1952] recognized following
events in the regeneration of ampulated
limbs.
 example : higher animals like salamander
and newts.

3. WOUND HEALING
 Injury to an organ result in exposure of the interior tissues to
the outside.
 Some cells in the injured region gets destroyed , there may be
bleeding at the injured surface.
 The blood soon clots and blocks further flow of blood to the
outside.
 Then the epidermal cells proliferate and migrate from all
sides towards the centre of the wound.
 Thus the epithelium forms a complete covering over the
injured tissue under the blood clot.
 The time needed for such a healing process depends on the
size of the wound , size of the regenerating animals and
external temperature.

4. DEMOLITION AND DEFENCE
 The next event in the destruction and
removal of the damaged tissue and foreign
elements such as germs.
 These are removed by autolysis and
phagocytosis by the blood cells.
 This is favoured by the increased blood
supply to this area.

5. DE-DIFFERENTIATION
 It refers to the reversion of differentiated cells to the
embryonic totipotent condition.
 Cells from the adjacent epidermis , muscles , nerves ,
cartilages , connective tissue etc. undergo de-
differentiation.
 The intracellular matrix of bones and cartilages becomes
dissolved and the osteoblasts and chondroblasts are set
free.
 They de-differentiate into totipotent cells.
 Similar de-differentiation occurs in muscle cells ,
connective tissues fibres and nerve cells .
 All these cells revert to embryonic totipotent state.

6. BLASTEMA FORMATION
 Next step is the formation of blastema or regeneration
bud.
 This is due to the accumulation of the de-differentiated
cells under the epithelial covering of the wound.
 As more and more cells aggregate below the epidermis , it
becomes pushed out and a conical projection appears.
 This bud like region consisting of an outer cap of
epidermis and central core of the de-differentiated cells
is called blastema or regeneration bud.

7. GROWTH
The blastema then grow in size.
This is caused by mitotic divisions of
the blastema cells.

8. RE-DIFFERENTIATION
 After attaining sufficient size , the blastema
passes into re-differentiation stage.
 The bone cells , cartilage cells , muscle cells ,
nerve cells and connective tissue cells are again
re-differentiated.
 They give rise to the bones , muscles, nerves and
connective tissue of the organ which is to be
regenerated.
 A blastema undergoes re-differentiation like a
limb-bud in the embryo.