1. Cleavage is the early mitotic divisions of the zygote that forms a hollow, multicellular blastocyst. The zygote undergoes a series of cleavages, reducing cell size and increasing metabolic rate. 2. Blastulation is the formation of the blastocyst from the morula. The outer cells of the morula form the trophoblast, which absorbs uterine fluid to form a blastocyst cavity. The inner cells remain as the embryoblast. 3. Implantation occurs when the blastocyst attaches to the uterine wall between 7-10 days after fertilization. The trophoblast cells invade the endometrium and secrete enzymes, forming

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.