Cleavage.ppt presented by dr hanif sheikh sb

embryology topic

1. Cleavage
Series of mitotic divisions in the early
embryo, producing a cluster of cells with
the same size as the original zygote.
Ends, with the formation of blastula.
Cleavage means “Partioning”

2. •Total mass remains same ---Blastomeres become
smaller and smaller.
•Nuclear to cytoplasmic ratio increases.
•Begins 30hrs after fertilization– ends as blastola forms
•Duration
•8 cell stage – cells are spherical, lossely arrange &
totipotent
•16 cell stage –cells becomes flatens on each other –
gap & tight junctions – compact ball --- Compaction
-------- involves cell surface glycoprotein, E-cadherin
•Compaction – segregates cells into:
Outer polar cells, &
Inner polar cells

4. Morula ( 4
th
day)
•16 cells or more --” Mulberry looking cell mass “
•Outer polar cells -- outer cell mass --trophoblast
•Inner polar cells - inner cell mass – embryoblast

5. Blastocyst
•4
th
Day --- Morula enters the uterus
•Fluid enters ---blastocele --- blastocyst
•Inner cell mass -- pushed to – Embryonic pole
Embryoblas &
Trophblast
EPF – determination
of pregnancy.
Zona pellucida disappear by hatching ---
Tyrosine like sub.-- prerequisite for implantation
6
th
Day Embryoblasts begin to implant.

8. Implantation

9. Implatation ---- 5 -- 6
th
day

10. Implataion conti.
•Initial attachment
L- selectin (trophoblast) --- carbohydrate
receptors present on the endometrium
•Further Atttachment & Invasion
Integrins ---- Laminin
•Migration
Integrins ---- Fibronection

11. •Time period ---6 to 10 days after ovulation
•(Implatation window 20
th
–23
rd
day)
•Complete at the end of 2
nd
wk
•Can be divided into three stages
•1) Ad plantation of blastocyst on
endometrium
•2) Adhesion of blastocyst on endometrium
•3) Invasion & embedding of blastocyst

12. Ad plantation (apposition)
•Endometrium-- secretary phase(20—24 day)
• Appearance of small elevations at the apical
pole of the epithelial endometrial cells –
absorption of uterine fluid which brings
blastocyst near endometrium
•Estrogen & Progesterone --- edema ---fills the
uterine cavity

13. Adhesion
• The microvilli on the surface of the outermost
trophoblast cells interact with the epithelial cells
of the uterus --------------through cell surface
glycoprotein,

14. Invasion & Embedding
•The trophoblast differentiates into:
•Outer syncytiotrophoblast ( S. T.)
•Inner cytotrophoblast ( C. T.)
•Lytic enz & secretary factors of S. T. –apoptosis
Penetration of stroma&eroding of walls of capp.

15. •In the middle of the 2nd week extracellular
vacuoles appear in the ST. They join together
forming lacunae.
•Erosion of maternal capp.--Lacuane filled with
blood–Utero placental circulation -- 13
th
day.

16. •Decidual reaction 9
th
Day Progesterone -- C. T.
stromal cells around implatation site become
metabolically & secretionally active and accumulate
glycogen & lipids & become polyhedral – Decidual
cells --- some degenerate & engulf by S. T. cells –
Nutrition for embryo & they also provide
immunologically privileged site for the conceptus.
•Maintenance of Pregnancy
S. T. cells secrete hcg ( positive hcg in maternal
serum –14
th
day) HCS & HPL ------ corpus luteum –
secrete estrogen and progesterone – responsible for
maintenance of pregnancy.

17. Abnormal Implatation
•Normally in posterior or anterior wall.
•(1) Withen uterus – cervics – Placenta Previa.
•(2) Extra uterine ( Ectopic Pregnancy)
A) Tubal – 95%
B) Pouch of Douglus
C) Peritoneum
D) Omentum – stone fetus
E) Ovary
Causes : mucosal adhesions due to PID.
•Complications
2
nd
month -- Rupture of ut tube - haemorrhage
-- embryo dies & sometime mother also.

18. Hydatidiform Mole
•Pregnancy with over development of trophoblasts &
extreme underdevelopment or absence of embryo
•Chorionic villi do not complete their development &
forms cystic swellings --- resembles bunches of
grapes– secrete high quantity of hcg.
•May produce benign or malignant tumors
Fate --- usually abort within first trimester

19. Causes of Hydatidiform Moles
•1) Monospermic (complete) or Dispermic Moles
( Partial) -- Mechanism of development.
•2) Embryo dies but trophoblasts proliferate
•3) After spontaneous abortion
•4) After normal delivery

20. •Hydatidiform Moles are of two types:
1) Partial Hydatidiform Mole
Shows some remnants of embryonic tissue.
Results from :-
Fertilization of normal ovum by two
spermatozoa– Triploid

21. 2) Complete Hydatidiform Mole
•Donot have any embryonic tissue
• Further sub divided into:
•A) Dispermic –----- empty ovum + two sperm
•B) Monospermic – empty ovum + one sperm
Followed by duplication resulting in 46
chromosomes.

22. •5% -- transform into Malignant and grow into
1) Invasive – invade surrounding tissues.
2) Choriocarcinoma – not only invading the
surrounding tissues but also spread to distant
organs.
•Metastasis
• by blood stream or lymphatics into ---
-- lungs, vagina, liver, bone,
intestine & brain
•Genome --- Paternal

23. Thankyou