Development of Embryo. Biology

1. Embryonic Development
By : Shashikant Neharkar
BBsc Nursing.

2. 1. Cleavage .
• It is process of early mitotic divisions of zygote
into hollow multicellular blastulla.
• Here cells are formed by clevage called
blastomeres cell.
• For each cleavage blastomere cells size get reduce
and metabolic rate increases .

3. Process of cleavage
• In human cleavage is holoblastic and planes may be
meridional , longitudinal, equatorial,and horizontal.
• 1st cleavage in the zygot is meridional occours about
30 hours after fertilization .
• It divides zygot into 2 blastomeres.
• 2nd cleavage is longitudinal , occours 30hrs after 1day
clevage .
• 3rd clevage is horizontal.
• Now embryo becomes 8 celled .

4. • Slowly slowly embryo pushesh towards uterus at
the end of 4th day after fertilization and becomes
16-32 celled.
• At these 16-32 celled stage embryo looks like
mulberry so it is called morulla .
• Morula has two types of cells, smaller cells
toward outer and larger inner cell called inner
mass of cell.
• Due to zona pellucida size of these is no change
but change occours overall from zygot to morulla .

5. *Blastulation *
• Blastulation is process of formation of the hollow
and multicellular blastocyst.
• These blastocyst remains floating in uterus .
• As we studied morulla has two types of cell from
these outer smaller cell of morulla form a layer
which called trophoblast.
• Now cells from these trophoblast starts to absorb
glycogen rich uterine milk .
• As more fluid gets absorbed a cavity begins to
develop in it called blastocyst cavity .

6. • Now larger cells of inner cell mass or embryoblast
remains attached to trophoblast .
• Due to unequal cells size and arrangement
blastocyst shows polarity ...
• The pole towards embryonal cells called
embryonal end and opposite to it called
abembryonal end .
• Zona pellucida layer of blastocyst prevent
implementation at abnormal site .
• At time of implantation zona pellucida repturs .

8. Implantation
• This process starts on 7th to 10th day after
fertilization.
• This implementation occour at fundus of uterus .
• Trophoblastic cells have ability to attach on
endometrium at embryonic pole / end .
• Now here rapid division in trophoblastic layer at
embryonic nob/ end takes place which gives two
types of cells .
• Outer multinucleated Syncytiotrophoblast and
inner layer of cells cytotrophoblasts .

9. • Syncytiotrophoblast gives out process which
invade the endometrium.
• They secret lytic enzymes to repture the
endometrial cells to make a burrow .
• In this burrow embryo gets implant by the end of
10th day after fertilization.